diff --git a/README.md b/README.md
index d2bb6b3..6d2050f 100644
--- a/README.md
+++ b/README.md
@@ -91,6 +91,16 @@ qc-cli infra destroy --yes                 Destroy stack without confirmation
 qc-cli infra destroy --delete-bucket-data  Destroy stack and delete S3 data
 ```
 
+### `upload`
+
+```
+qc-cli upload <file>                 Upload a single file to S3
+qc-cli upload <dir>                  Upload all files in a directory tree to S3
+qc-cli upload <file> --s3-key <key>  Upload a file to a custom S3 key
+```
+
+Uploads use `s3.bucket` and `s3.data_prefix` from `config.yaml`. File uploads default to `s3://<bucket>/<data_prefix>/<filename>`. Directory uploads are recursive, preserve paths relative to the uploaded directory, and place files under `s3://<bucket>/<data_prefix>/`.
+
 ## AWS permissions required
 
 The IAM user or role running the CLI needs:
diff --git a/src/aws/s3.py b/src/aws/s3.py
new file mode 100644
index 0000000..9a2141a
--- /dev/null
+++ b/src/aws/s3.py
@@ -0,0 +1,51 @@
+from collections.abc import Callable
+from concurrent.futures import ThreadPoolExecutor, as_completed
+from pathlib import Path
+
+import boto3
+from mypy_boto3_s3 import S3Client
+
+
+def _client(region: str, profile: str) -> S3Client:
+    return boto3.Session(profile_name=profile, region_name=region).client("s3")
+
+
+def upload_file(
+    region: str,
+    profile: str,
+    bucket: str,
+    local_path: str,
+    s3_key: str,
+) -> str:
+    _client(region, profile).upload_file(local_path, bucket, s3_key)
+    return f"s3://{bucket}/{s3_key}"
+
+
+def upload_dir(
+    region: str,
+    profile: str,
+    bucket: str,
+    local_dir: str,
+    s3_prefix: str,
+    on_progress: Callable[[], None] | None = None,
+) -> int:
+    root = Path(local_dir)
+    files = [file for file in root.rglob("*") if file.is_file()]
+    if not files:
+        return 0
+
+    client = _client(region, profile)
+    prefix = s3_prefix.rstrip("/")
+
+    def upload_one(file_path: Path) -> None:
+        key = f"{prefix}/{file_path.relative_to(root)}"
+        client.upload_file(str(file_path), bucket, key)
+        if on_progress:
+            on_progress()
+
+    with ThreadPoolExecutor(max_workers=10) as pool:
+        futures = [pool.submit(upload_one, file) for file in files]
+        for future in as_completed(futures):
+            future.result()
+
+    return len(files)
diff --git a/src/main.py b/src/main.py
index dd8cd9a..3414744 100644
--- a/src/main.py
+++ b/src/main.py
@@ -3,8 +3,11 @@ from pathlib import Path
 import typer
 import yaml
 from rich.console import Console
+from rich.progress import BarColumn, Progress, SpinnerColumn, TaskProgressColumn, TextColumn
 
+from src.aws import s3 as s3_ops
 from src.commands import infra
+from src.commands.utils import CONFIG_OPT, load_cfg
 from src.config import Config
 
 app = typer.Typer(
@@ -34,3 +37,64 @@ def init(
 
     console.print(f"[green]✓[/green] Config written to [bold]{dest}[/bold]")
     console.print("Edit it (especially [cyan]s3.bucket[/cyan]) before running other commands.")
+
+
+@app.command()
+def upload(
+    path: Path = typer.Argument(..., help="Local file or directory to upload"),
+    s3_key: str | None = typer.Option(None, "--s3-key", help="S3 key for file uploads"),
+    config: str = CONFIG_OPT,
+) -> None:
+    """Upload a local file or directory to S3."""
+    cfg = load_cfg(config)
+
+    if path.is_file():
+        key = s3_key or f"{cfg.s3.data_prefix.rstrip('/')}/{path.name}"
+        try:
+            with console.status(f"Uploading {path.name}..."):
+                uri = s3_ops.upload_file(cfg.aws.region, cfg.aws.profile, cfg.s3.bucket, str(path), key)
+        except Exception as e:
+            console.print(f"[red]Upload failed: {e}[/red]")
+            raise typer.Exit(1)
+
+        console.print(f"[green]✓[/green] {path.name} -> {uri}")
+        return
+
+    if path.is_dir():
+        if s3_key is not None:
+            console.print("[red]--s3-key can only be used when uploading a single file.[/red]")
+            raise typer.Exit(1)
+
+        files = [file for file in path.rglob("*") if file.is_file()]
+        if not files:
+            console.print("[yellow]No files found in directory.[/yellow]")
+            raise typer.Exit(0)
+
+        prefix = cfg.s3.data_prefix
+        console.print(f"Uploading {len(files)} files to s3://{cfg.s3.bucket}/{prefix.rstrip('/')}/")
+        try:
+            with Progress(
+                SpinnerColumn(),
+                TextColumn("[progress.description]{task.description}"),
+                BarColumn(),
+                TaskProgressColumn(),
+                console=console,
+            ) as progress:
+                task = progress.add_task("Uploading...", total=len(files))
+                count = s3_ops.upload_dir(
+                    cfg.aws.region,
+                    cfg.aws.profile,
+                    cfg.s3.bucket,
+                    str(path),
+                    prefix,
+                    on_progress=lambda: progress.advance(task),
+                )
+        except Exception as e:
+            console.print(f"[red]Upload failed: {e}[/red]")
+            raise typer.Exit(1)
+
+        console.print(f"[green]✓[/green] Uploaded {count} files to s3://{cfg.s3.bucket}/{prefix.rstrip('/')}/")
+        return
+
+    console.print(f"[red]Path not found: {path}[/red]")
+    raise typer.Exit(1)