diff --git a/admin/setup_mvp.php b/admin/setup_mvp.php
index d7c59ae..3421f0e 100644
--- a/admin/setup_mvp.php
+++ b/admin/setup_mvp.php
@@ -156,9 +156,6 @@ foreach ($lines_by_section as $section_code => $lines) {
         
         // Use Dolibarr's native multi-select with search functionality
         print $form->multiselectarray('account_codes_' . $line, $account_options, $selected_accounts, 0, 0, '', 0, '200px');
-        
-        // Add helper text
-        print '<br><small>' . $langs->trans("MultiSelectHelp") . '</small>';
         print '</td>';
         print '</tr>';
     }
diff --git a/core/class/declarationtva_config.class.php b/core/class/declarationtva_config.class.php
index e69de29..583ae01 100644
--- a/core/class/declarationtva_config.class.php
+++ b/core/class/declarationtva_config.class.php
@@ -0,0 +1,425 @@
+<?php
+/**
+ * DeclarationTVA_Config Class
+ * Configuration management for DeclarationTVA module
+ * MVP Version - Phase 1
+ */
+
+class DeclarationTVA_Config
+{
+    /**
+     * @var DoliDB Database handler
+     */
+    public $db;
+
+    /**
+     * @var int Entity ID
+     */
+    public $entity;
+
+    /**
+     * @var string Error message
+     */
+    public $error;
+
+    /**
+     * Constructor
+     *
+     * @param DoliDB $db Database handler
+     * @param int $entity Entity ID
+     */
+    public function __construct($db, $entity = 1)
+    {
+        $this->db = $db;
+        $this->entity = $entity;
+    }
+
+    /**
+     * Get configuration value
+     *
+     * @param string $key Configuration key
+     * @param mixed $default Default value
+     * @return mixed Configuration value
+     */
+    public function get($key, $default = null)
+    {
+        $sql = "SELECT config_value FROM " . MAIN_DB_PREFIX . "declarationtva_config 
+                WHERE entity = " . $this->entity . " AND config_key = '" . $this->db->escape($key) . "'";
+
+        $result = $this->db->query($sql);
+        if ($result && $this->db->num_rows($result) > 0) {
+            $obj = $this->db->fetch_object($result);
+            return $obj->config_value;
+        }
+
+        return $default;
+    }
+
+    /**
+     * Set configuration value
+     *
+     * @param string $key Configuration key
+     * @param mixed $value Configuration value
+     * @return bool Success
+     */
+    public function set($key, $value)
+    {
+        $sql = "INSERT INTO " . MAIN_DB_PREFIX . "declarationtva_config 
+                (entity, config_key, config_value, created_date) 
+                VALUES (" . $this->entity . ", '" . $this->db->escape($key) . "', 
+                '" . $this->db->escape($value) . "', NOW()) 
+                ON DUPLICATE KEY UPDATE config_value = '" . $this->db->escape($value) . "'";
+
+        $result = $this->db->query($sql);
+        return $result !== false;
+    }
+
+    /**
+     * Get account mapping for a CA-3 line
+     *
+     * @param string $ca3_line CA-3 line code
+     * @return array|false Account mapping or false if not found
+     */
+    public function getAccountMapping($ca3_line)
+    {
+        $sql = "SELECT * FROM " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                WHERE entity = " . $this->entity . " AND ca3_line = '" . $this->db->escape($ca3_line) . "'";
+
+        $result = $this->db->query($sql);
+        if ($result && $this->db->num_rows($result) > 0) {
+            return $this->db->fetch_array($result);
+        }
+
+        return false;
+    }
+
+    /**
+     * Update account mapping for multiple accounts
+     *
+     * @param string $ca3_line CA-3 line code
+     * @param array $account_codes Array of account codes
+     * @return bool Success
+     */
+    public function updateAccountMapping($ca3_line, $account_codes)
+    {
+        // First, deactivate all existing mappings for this CA-3 line
+        $sql = "UPDATE " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                SET is_active = 0 
+                WHERE entity = " . $this->entity . " AND ca3_line = '" . $this->db->escape($ca3_line) . "'";
+        $this->db->query($sql);
+        
+        // Then insert/activate new mappings
+        if (!empty($account_codes)) {
+            foreach ($account_codes as $account_code) {
+                if (!empty($account_code)) {
+                    // Check if mapping already exists
+                    $check_sql = "SELECT id FROM " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                                 WHERE entity = " . $this->entity . " 
+                                 AND ca3_line = '" . $this->db->escape($ca3_line) . "' 
+                                 AND account_code = '" . $this->db->escape($account_code) . "'";
+                    $check_result = $this->db->query($check_sql);
+                    
+                    if ($check_result && $this->db->num_rows($check_result) > 0) {
+                        // Update existing mapping
+                        $sql = "UPDATE " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                                SET is_active = 1 
+                                WHERE entity = " . $this->entity . " 
+                                AND ca3_line = '" . $this->db->escape($ca3_line) . "' 
+                                AND account_code = '" . $this->db->escape($account_code) . "'";
+                        $this->db->query($sql);
+                    } else {
+                        // Insert new mapping
+                        $sql = "INSERT INTO " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                                (entity, ca3_line, account_code, account_label, vat_rate, is_active, created_date) 
+                                VALUES (" . $this->entity . ", '" . $this->db->escape($ca3_line) . "', 
+                                '" . $this->db->escape($account_code) . "', '', 0, 1, NOW())";
+                        $this->db->query($sql);
+                    }
+                }
+            }
+        }
+        
+        return true;
+    }
+
+    /**
+     * Get all account mappings
+     *
+     * @return array Account mappings
+     */
+    public function getAllAccountMappings()
+    {
+        $sql = "SELECT * FROM " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                WHERE entity = " . $this->entity . " AND is_active = 1 
+                ORDER BY ca3_line";
+
+        $result = $this->db->query($sql);
+        $mappings = array();
+
+        if ($result) {
+            while ($obj = $this->db->fetch_object($result)) {
+                $mappings[] = array(
+                    'rowid' => $obj->rowid,
+                    'ca3_line' => $obj->ca3_line,
+                    'account_code' => $obj->account_code,
+                    'account_label' => $obj->account_label,
+                    'vat_rate' => $obj->vat_rate,
+                    'is_active' => $obj->is_active
+                );
+            }
+        }
+
+        return $mappings;
+    }
+
+    /**
+     * Get account mappings grouped by CA-3 line
+     *
+     * @return array Account mappings grouped by CA-3 line
+     */
+    public function getAccountMappingsByLine()
+    {
+        $sql = "SELECT ca3_line, account_code FROM " . MAIN_DB_PREFIX . "declarationtva_account_mappings 
+                WHERE entity = " . $this->entity . " AND is_active = 1 
+                ORDER BY ca3_line, account_code";
+
+        $result = $this->db->query($sql);
+        $mappings = array();
+
+        if ($result) {
+            while ($obj = $this->db->fetch_object($result)) {
+                if (!isset($mappings[$obj->ca3_line])) {
+                    $mappings[$obj->ca3_line] = array();
+                }
+                $mappings[$obj->ca3_line][] = $obj->account_code;
+            }
+        }
+
+        return $mappings;
+    }
+
+    /**
+     * Get available accounting accounts from Dolibarr
+     *
+     * @return array Accounting accounts
+     */
+    public function getAccountingAccounts()
+    {
+        $sql = "SELECT account_number, label FROM " . MAIN_DB_PREFIX . "accounting_account 
+                WHERE active = 1 
+                ORDER BY account_number";
+
+        $result = $this->db->query($sql);
+        $accounts = array();
+
+        if ($result) {
+            while ($obj = $this->db->fetch_object($result)) {
+                $accounts[] = array(
+                    'account_number' => $obj->account_number,
+                    'label' => $obj->label
+                );
+            }
+        }
+
+        return $accounts;
+    }
+
+    /**
+     * Get CA-3 line definitions (Notice 4722 - Latest Official Structure)
+     *
+     * @return array CA-3 line definitions
+     */
+    public function getCA3LineDefinitions()
+    {
+        return array(
+            // A. Opérations imposables (Taxable Operations) - Notice 4722
+            'A1' => array(
+                'label' => 'Montant HT des opérations imposables normales (biens + services imposables en France à 20%, 10%, 5,5%, 2,1%)',
+                'type' => 'base',
+                'section' => 'A',
+                'description' => 'HT amount of all taxable operations that form normal sales (goods + services taxable in France at 20%, 10%, 5,5%, 2,1%)',
+                'pcg_accounts' => 'Sales: 7xxxx; VAT: 44571x / 44572x / 44573x / 44574x'
+            ),
+            'A2' => array(
+                'label' => 'Montant HT des opérations imposables spéciales ne relevant pas du CA courant (cessions d\'immobilisations, livraisons à soi-même)',
+                'type' => 'base',
+                'section' => 'A',
+                'description' => 'HT amount of special taxable operations not part of ordinary turnover (e.g. cessions d\'immobilisations, livraisons à soi-même)',
+                'pcg_accounts' => '775xxx (gains on disposal), 72xxx (production immobilisée), VAT: 44571x'
+            ),
+            'A3' => array(
+                'label' => 'Montant HT des services achetés à des prestataires non établis en France mais imposables en France (autoliquidation services étrangers)',
+                'type' => 'base',
+                'section' => 'A',
+                'description' => 'HT amount of services purchased from providers not established in France but taxable in France (reverse charge for foreign services)',
+                'pcg_accounts' => '6xxxx (services purchased), 4452xxx (TVA due autoliquidée)'
+            ),
+            'A4' => array(
+                'label' => 'Montant HT des importations imposables en France (hors UE), à l\'exclusion des produits pétroliers',
+                'type' => 'base',
+                'section' => 'A',
+                'description' => 'HT amount of imports taxable in France (non-EU), excluding petroleum products',
+                'pcg_accounts' => '6xxxx / 2xxxx purchases or assets; VAT: 4452xxx (import VAT)'
+            ),
+            'A5' => array(
+                'label' => 'Montant HT des opérations imposables à la sortie d\'un régime fiscal suspensif (régimes douaniers, zones franches, etc.)',
+                'type' => 'base',
+                'section' => 'A',
+                'description' => 'HT amount of taxable operations at exit from a suspensive fiscal regime (customs regimes, free zones, etc.)',
+                'pcg_accounts' => 'Specific 6xxxx/2xxxx depending on goods; VAT: 4452xxx'
+            ),
+            
+            // B. Décompte de la TVA due (VAT Due Calculation) - Notice 4722
+            '08' => array(
+                'label' => 'TVA due au taux de 20%',
+                'type' => 'vat',
+                'section' => 'B',
+                'description' => 'VAT amounts due, calculated on A1/A2 bases at 20% rate',
+                'pcg_accounts' => '44571x (TVA collectée à 20%)'
+            ),
+            '09' => array(
+                'label' => 'TVA due au taux de 10%',
+                'type' => 'vat',
+                'section' => 'B',
+                'description' => 'VAT amounts due, calculated on A1/A2 bases at 10% rate',
+                'pcg_accounts' => '44572x (TVA collectée à 10%)'
+            ),
+            '9B' => array(
+                'label' => 'TVA due aux taux réduits (5,5% et 2,1%)',
+                'type' => 'vat',
+                'section' => 'B',
+                'description' => 'VAT amounts due, calculated on A1/A2 bases at reduced rates (5,5% and 2,1%)',
+                'pcg_accounts' => '44573x (5,5%) / 44574x (2,1%) (TVA collectée aux taux réduits)'
+            ),
+            '17' => array(
+                'label' => 'TVA due au titre des acquisitions intracommunautaires (autoliquidation)',
+                'type' => 'vat',
+                'section' => 'B',
+                'description' => 'VAT due on intra-EU acquisitions (autoliquidation)',
+                'pcg_accounts' => '4452xxx (TVA due intracommunautaire)'
+            ),
+            
+            // C. Décompte de la TVA déductible (Deductible VAT Calculation) - Notice 4722
+            '20' => array(
+                'label' => 'TVA déductible sur immobilisations',
+                'type' => 'vat',
+                'section' => 'C',
+                'description' => 'Deductible VAT on capital goods (fixed assets)',
+                'pcg_accounts' => '44562x (TVA déductible sur immobilisations)'
+            ),
+            '21' => array(
+                'label' => 'TVA déductible sur autres biens et services',
+                'type' => 'vat',
+                'section' => 'C',
+                'description' => 'Deductible VAT on other goods and services (operating expenses)',
+                'pcg_accounts' => '44566x (TVA déductible sur autres biens et services)'
+            ),
+            '22' => array(
+                'label' => 'TVA déductible sur importations',
+                'type' => 'vat',
+                'section' => 'C',
+                'description' => 'Deductible VAT on imports',
+                'pcg_accounts' => '44566x / 44562x (TVA déductible sur importations)'
+            ),
+            
+            // D. Résultat (Result) - Notice 4722
+            '25' => array(
+                'label' => 'TVA brute due (Total TVA due)',
+                'type' => 'vat',
+                'section' => 'D',
+                'description' => 'Total VAT due (sum of all VAT due amounts)',
+                'pcg_accounts' => 'Sum of 08 + 09 + 9B + 17'
+            ),
+            '26' => array(
+                'label' => 'TVA déductible totale (Total deductible VAT)',
+                'type' => 'vat',
+                'section' => 'D',
+                'description' => 'Total deductible VAT (sum of all deductible VAT amounts)',
+                'pcg_accounts' => 'Sum of 20 + 21 + 22'
+            ),
+            '28' => array(
+                'label' => 'TVA nette à payer',
+                'type' => 'vat',
+                'section' => 'D',
+                'description' => 'Net VAT to pay (if total due > total deductible)',
+                'pcg_accounts' => '445510 (État - TVA à décaisser)'
+            ),
+            '29' => array(
+                'label' => 'Crédit de TVA à reporter ou remboursement',
+                'type' => 'vat',
+                'section' => 'D',
+                'description' => 'VAT credit to carry forward or refund (if total deductible > total due)',
+                'pcg_accounts' => '445670 (État - Crédit de TVA à reporter ou rembourser)'
+            )
+        );
+    }
+
+    /**
+     * Get CA-3 section headers (Notice 4722)
+     *
+     * @return array Section headers
+     */
+    public function getCA3SectionHeaders()
+    {
+        return array(
+            'A' => array(
+                'title' => 'A. Opérations imposables (Taxable Operations)',
+                'description' => 'HT amounts of all taxable operations according to Notice 4722 (3310-CA3-SD)',
+                'notice' => 'Notice 4722 - Summary Table CA3 (3310-CA3-SD)'
+            ),
+            'B' => array(
+                'title' => 'B. Décompte de la TVA due (VAT Due Calculation)',
+                'description' => 'VAT amounts due, calculated on A1/A2 bases per applicable rate',
+                'notice' => 'Notice 4722 - VAT Due Calculation'
+            ),
+            'C' => array(
+                'title' => 'C. Décompte de la TVA déductible (Deductible VAT Calculation)',
+                'description' => 'VAT amounts that can be deducted from purchases and expenses',
+                'notice' => 'Notice 4722 - Deductible VAT Calculation'
+            ),
+            'D' => array(
+                'title' => 'D. Résultat (Result)',
+                'description' => 'Final calculation: net VAT to pay or credit to carry forward',
+                'notice' => 'Notice 4722 - Final Result'
+            )
+        );
+    }
+
+    /**
+     * Get supported VAT rates
+     *
+     * @return array VAT rates
+     */
+    public function getVATRates()
+    {
+        return array(
+            '20.00' => '20%',
+            '10.00' => '10%',
+            '5.50' => '5.5%',
+            '2.10' => '2.1%',
+            '0.00' => '0%'
+        );
+    }
+
+    /**
+     * Validate account mapping
+     *
+     * @param string $ca3_line CA-3 line code
+     * @param string $account_code Account code
+     * @return bool Valid
+     */
+    public function validateAccountMapping($ca3_line, $account_code)
+    {
+        // Check if account exists in Dolibarr
+        $sql = "SELECT COUNT(*) as count FROM " . MAIN_DB_PREFIX . "accounting_account 
+                WHERE account_number = '" . $this->db->escape($account_code) . "' AND active = 1";
+
+        $result = $this->db->query($sql);
+        if ($result && $this->db->num_rows($result) > 0) {
+            $obj = $this->db->fetch_object($result);
+            return $obj->count > 0;
+        }
+
+        return false;
+    }
+}
diff --git a/langs/en_US/declarationtva.lang b/langs/en_US/declarationtva.lang
index 40f967e..05209a6 100644
--- a/langs/en_US/declarationtva.lang
+++ b/langs/en_US/declarationtva.lang
@@ -368,6 +368,5 @@ PCGAccounts = PCG Accounts
 AccountSelection = Account Selection
 SelectedAccounts = Selected Accounts
 AccountCount = Account Count
-MultiSelectHelp = Hold Ctrl (or Cmd on Mac) to select multiple accounts
 ErrorCSRFToken = Security token error. Please try again.
 NoChangesDetected = No changes detected in the configuration.
diff --git a/langs/fr_FR/declarationtva.lang b/langs/fr_FR/declarationtva.lang
index 3318a9b..bf149e5 100644
--- a/langs/fr_FR/declarationtva.lang
+++ b/langs/fr_FR/declarationtva.lang
@@ -357,6 +357,5 @@ PCGAccounts = Comptes PCG
 AccountSelection = Sélection de comptes
 SelectedAccounts = Comptes sélectionnés
 AccountCount = Nombre de comptes
-MultiSelectHelp = Maintenez Ctrl (ou Cmd sur Mac) pour sélectionner plusieurs comptes
 ErrorCSRFToken = Erreur de jeton de sécurité. Veuillez réessayer.
 NoChangesDetected = Aucun changement détecté dans la configuration.