diff --git a/src/components/App/App.tsx b/src/components/App/App.tsx
index 160197e..0fa1453 100644
--- a/src/components/App/App.tsx
+++ b/src/components/App/App.tsx
@@ -4,15 +4,18 @@
  * Main application layout
  */
 
-import { useEffect } from 'react';
+import { useEffect, useState } from 'react';
 import { PedigreeCanvas } from '../PedigreeCanvas/PedigreeCanvas';
 import { Toolbar } from '../Toolbar/Toolbar';
 import { PropertyPanel } from '../PropertyPanel/PropertyPanel';
 import { RelationshipPanel } from '../RelationshipPanel/RelationshipPanel';
 import { FilePanel } from '../FilePanel/FilePanel';
+import { WelcomeModal } from '../WelcomeModal/WelcomeModal';
 import { usePedigreeStore, useTemporalStore } from '@/store/pedigreeStore';
 import styles from './App.module.css';
 
+const WELCOME_DISMISSED_KEY = 'pedigree-draw-welcome-dismissed';
+
 export function App() {
   const {
     clearSelection,
@@ -23,6 +26,15 @@ export function App() {
   } = usePedigreeStore();
   const temporal = useTemporalStore();
 
+  // Welcome modal state - check localStorage on init
+  const [showWelcome, setShowWelcome] = useState(() => {
+    return localStorage.getItem(WELCOME_DISMISSED_KEY) !== 'true';
+  });
+
+  const handleCloseWelcome = () => {
+    setShowWelcome(false);
+  };
+
   // Keyboard shortcuts
   useEffect(() => {
     const handleKeyDown = (e: KeyboardEvent) => {
@@ -85,6 +97,8 @@ export function App() {
         <span>Pedigree Draw - For genetic counselors and bioinformatics professionals</span>
         <span>NSGC Standard Symbols</span>
       </footer>
+
+      {showWelcome && <WelcomeModal onClose={handleCloseWelcome} />}
     </div>
   );
 }
diff --git a/src/components/WelcomeModal/WelcomeModal.module.css b/src/components/WelcomeModal/WelcomeModal.module.css
new file mode 100644
index 0000000..d365272
--- /dev/null
+++ b/src/components/WelcomeModal/WelcomeModal.module.css
@@ -0,0 +1,92 @@
+.overlay {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.6);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 1000;
+  padding: 20px;
+}
+
+.modal {
+  background: white;
+  border-radius: 12px;
+  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
+  max-width: 520px;
+  width: 100%;
+  padding: 32px;
+  max-height: 90vh;
+  overflow-y: auto;
+}
+
+.title {
+  font-size: 24px;
+  font-weight: 600;
+  color: #1976D2;
+  text-align: center;
+  margin: 0 0 24px 0;
+}
+
+.section {
+  margin-bottom: 24px;
+}
+
+.sectionTitle {
+  font-size: 14px;
+  font-weight: 600;
+  color: #666;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  margin: 0 0 12px 0;
+  padding-bottom: 8px;
+  border-bottom: 1px solid #eee;
+}
+
+.paragraph {
+  font-size: 14px;
+  line-height: 1.6;
+  color: #333;
+  margin: 0 0 12px 0;
+}
+
+.paragraph:last-child {
+  margin-bottom: 0;
+}
+
+.button {
+  display: block;
+  width: 100%;
+  padding: 14px 24px;
+  background: #1976D2;
+  color: white;
+  border: none;
+  border-radius: 8px;
+  font-size: 16px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: background 0.2s ease;
+}
+
+.button:hover {
+  background: #1565C0;
+}
+
+.button:active {
+  background: #0D47A1;
+}
+
+/* Responsive design */
+@media (max-width: 600px) {
+  .modal {
+    padding: 24px;
+  }
+
+  .title {
+    font-size: 20px;
+  }
+
+  .paragraph {
+    font-size: 13px;
+  }
+}
diff --git a/src/components/WelcomeModal/WelcomeModal.tsx b/src/components/WelcomeModal/WelcomeModal.tsx
new file mode 100644
index 0000000..5ad5a92
--- /dev/null
+++ b/src/components/WelcomeModal/WelcomeModal.tsx
@@ -0,0 +1,75 @@
+/**
+ * WelcomeModal Component
+ *
+ * Displays author information and privacy policy on first visit.
+ * Uses localStorage to remember dismissal.
+ * Automatically detects browser language for Chinese/English content.
+ */
+
+import styles from './WelcomeModal.module.css';
+
+interface WelcomeModalProps {
+  onClose: () => void;
+}
+
+const isChineseLocale = (): boolean => {
+  const lang = navigator.language || (navigator.languages?.[0]) || 'en';
+  return lang.toLowerCase().startsWith('zh');
+};
+
+export function WelcomeModal({ onClose }: WelcomeModalProps) {
+  const isChinese = isChineseLocale();
+
+  const content = isChinese ? {
+    title: '歡迎使用 Pedigree Draw',
+    aboutTitle: '關於本專案',
+    aboutContent: [
+      '本專案由一位患有 Usher syndrome 的作者所建立。',
+      '建立此工具的動機是為了支援遺傳學、系譜學和 Bioinformatics 領域的研究，並探索視覺化工具如何幫助理解遺傳性疾病。',
+      '作者明確支持與 Usher syndrome 及其他遺傳疾病相關的研究，並希望此專案能以某種方式為 Bioinformatics 研究社群做出貢獻。',
+    ],
+    privacyTitle: '隱私政策',
+    privacyContent: '本網站不搜集任何使用者資料，也不儲存任何資料。所有操作僅在您的瀏覽器中進行，關閉頁面後資料即消失。',
+    buttonText: '我了解，開始使用',
+  } : {
+    title: 'Welcome to Pedigree Draw',
+    aboutTitle: 'About This Project',
+    aboutContent: [
+      'This project is created by an author with Usher syndrome.',
+      'The motivation behind this work is to support research in genetics, genealogy, and bioinformatics, and to explore how visualization tools may assist in understanding hereditary conditions.',
+      'The author explicitly supports research related to Usher syndrome and other genetic disorders, and hopes this project may contribute, even in a small way, to the bioinformatics research community.',
+    ],
+    privacyTitle: 'Privacy Policy',
+    privacyContent: 'This website does not collect any user data or store any information. All operations are performed locally in your browser. Data will be lost when you close the page.',
+    buttonText: 'I Understand, Let\'s Start',
+  };
+
+  const handleClose = () => {
+    localStorage.setItem('pedigree-draw-welcome-dismissed', 'true');
+    onClose();
+  };
+
+  return (
+    <div className={styles.overlay} onClick={handleClose}>
+      <div className={styles.modal} onClick={(e) => e.stopPropagation()}>
+        <h1 className={styles.title}>{content.title}</h1>
+
+        <section className={styles.section}>
+          <h2 className={styles.sectionTitle}>{content.aboutTitle}</h2>
+          {content.aboutContent.map((paragraph, index) => (
+            <p key={index} className={styles.paragraph}>{paragraph}</p>
+          ))}
+        </section>
+
+        <section className={styles.section}>
+          <h2 className={styles.sectionTitle}>{content.privacyTitle}</h2>
+          <p className={styles.paragraph}>{content.privacyContent}</p>
+        </section>
+
+        <button className={styles.button} onClick={handleClose}>
+          {content.buttonText}
+        </button>
+      </div>
+    </div>
+  );
+}