diff --git a/.changeset/mobile-enter-newline.md b/.changeset/mobile-enter-newline.md
new file mode 100644
index 0000000..fd2296b
--- /dev/null
+++ b/.changeset/mobile-enter-newline.md
@@ -0,0 +1,5 @@
+---
+"@jmfederico/pi-web": patch
+---
+
+Keep Enter/Return in the mobile chat composer for new lines, and send messages there only from the send button.
diff --git a/src/client/src/components/PromptEditor.ts b/src/client/src/components/PromptEditor.ts
index a5dc404..944c3a9 100644
--- a/src/client/src/components/PromptEditor.ts
+++ b/src/client/src/components/PromptEditor.ts
@@ -13,6 +13,7 @@ import { machineSessionKey } from "../machineKeys";
 import { detectPromptCompletionTrigger, fileCompletionInsertText, type PromptCompletionTrigger } from "../promptCompletions";
 import { clearDraft, loadDraft, saveDraft } from "../promptDraftStorage";
 import { loadAttachmentDelivery, saveAttachmentDelivery } from "../attachmentPreferences";
+import { createMobilePromptEnterMedia, shouldSendPromptOnEnter } from "../promptEnterBehavior";
 import { promptEditorStyles, type CompletionItem } from "./shared";
 import { renderAttachIcon, renderSendIcon, renderQueueIcon, renderSteerIcon, renderStopIcon, renderThinkingGauge } from "./promptEditorIcons";
 import { thinkingGauge, thinkingLevelLabel } from "../../../shared/thinkingLevels";
@@ -59,6 +60,7 @@ export class PromptEditor extends LitElement {
   private editor: EditorView | undefined;
   private readonly editableCompartment = new Compartment();
   private readonly readOnlyCompartment = new Compartment();
+  private readonly mobilePromptEnterMedia = createMobilePromptEnterMedia();
 
   protected override willUpdate(changed: PropertyValues<this>) {
     if (!changed.has("sessionId") && !changed.has("machineId")) return;
@@ -238,7 +240,7 @@ export class PromptEditor extends LitElement {
             { key: "ArrowDown", run: () => this.moveCompletion(1) },
             { key: "ArrowUp", run: () => this.moveCompletion(-1) },
             { key: "Escape", run: () => this.closeCompletions() },
-            { key: "Enter", run: () => this.handleEditorEnter() },
+            { key: "Enter", run: (view) => this.handleEditorEnter(view) },
             { key: "Shift-Enter", run: (view) => insertNewlineContinueMarkup(view) || insertNewlineAndIndent(view) },
             { key: "Tab", run: (view) => this.handleEditorTab(view) },
             { key: "Shift-Tab", run: (view) => indentWithTab.shift?.(view) ?? false },
@@ -335,12 +337,15 @@ export class PromptEditor extends LitElement {
     return true;
   }
 
-  private handleEditorEnter(): boolean {
+  private handleEditorEnter(view: EditorView): boolean {
     if (this.completions.length) {
       const completion = this.completions[this.selectedIndex];
       if (completion !== undefined) this.pick(completion);
       return true;
     }
+    if (!shouldSendPromptOnEnter(this.mobilePromptEnterMedia)) {
+      return insertNewlineContinueMarkup(view) || insertNewlineAndIndent(view);
+    }
     this.send(this.canSteer || this.isCompacting ? "followUp" : undefined);
     return true;
   }
diff --git a/src/client/src/promptEnterBehavior.test.ts b/src/client/src/promptEnterBehavior.test.ts
new file mode 100644
index 0000000..bb5eabe
--- /dev/null
+++ b/src/client/src/promptEnterBehavior.test.ts
@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+import { MOBILE_PROMPT_ENTER_MEDIA_QUERY, shouldSendPromptOnEnter, type PromptEnterMedia } from "./promptEnterBehavior";
+
+describe("promptEnterBehavior", () => {
+  it("uses the expected mobile media query", () => {
+    expect(MOBILE_PROMPT_ENTER_MEDIA_QUERY).toBe("(pointer: coarse), (max-width: 760px)");
+  });
+
+  it("sends on Enter outside the mobile environment", () => {
+    expect(shouldSendPromptOnEnter({ matches: false } satisfies PromptEnterMedia)).toBe(true);
+    expect(shouldSendPromptOnEnter(undefined)).toBe(true);
+  });
+
+  it("keeps Enter as a newline in the mobile environment", () => {
+    expect(shouldSendPromptOnEnter({ matches: true } satisfies PromptEnterMedia)).toBe(false);
+  });
+});
diff --git a/src/client/src/promptEnterBehavior.ts b/src/client/src/promptEnterBehavior.ts
new file mode 100644
index 0000000..faef8ac
--- /dev/null
+++ b/src/client/src/promptEnterBehavior.ts
@@ -0,0 +1,11 @@
+export const MOBILE_PROMPT_ENTER_MEDIA_QUERY = "(pointer: coarse), (max-width: 760px)";
+
+export type PromptEnterMedia = Pick<MediaQueryList, "matches">;
+
+export function createMobilePromptEnterMedia(): PromptEnterMedia | undefined {
+  return typeof window !== "undefined" && "matchMedia" in window ? window.matchMedia(MOBILE_PROMPT_ENTER_MEDIA_QUERY) : undefined;
+}
+
+export function shouldSendPromptOnEnter(media = createMobilePromptEnterMedia()): boolean {
+  return media?.matches !== true;
+}