diff --git a/doc/api/index.rst b/doc/api/index.rst
index 5a69dab..c8b2e3e 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -11,22 +11,37 @@ Input and output
 ----------------
 
 .. autosummary::
-   :toctree: generated/
+    :toctree: generated/
 
     load_scene
     save_scene
     load_panchromatic
 
-Processing
-----------
+Visualization
+-------------
 
 .. autosummary::
-   :toctree: generated/
+    :toctree: generated/
 
     composite
-    pansharpen
     equalize_histogram
     adjust_l1_colors
+
+Indices
+-------
+
+.. autosummary::
+    :toctree: generated/
+
+    ndvi
+
+Processing
+----------
+
+.. autosummary::
+    :toctree: generated/
+
+    pansharpen
     interpolate_missing
 
 Sample datasets
diff --git a/xlandsat/__init__.py b/xlandsat/__init__.py
index 0748713..f95519f 100644
--- a/xlandsat/__init__.py
+++ b/xlandsat/__init__.py
@@ -4,6 +4,7 @@
 from . import datasets
 from ._composite import composite
 from ._enhancement import adjust_l1_colors, equalize_histogram
+from ._indices import ndvi
 from ._interpolation import interpolate_missing
 from ._io import load_panchromatic, load_scene, save_scene
 from ._pansharpen import pansharpen
diff --git a/xlandsat/_indices.py b/xlandsat/_indices.py
new file mode 100644
index 0000000..f2237f8
--- /dev/null
+++ b/xlandsat/_indices.py
@@ -0,0 +1,41 @@
+# Copyright (c) 2022 The xlandsat developers.
+# Distributed under the terms of the MIT License.
+# SPDX-License-Identifier: MIT
+"""
+Calculate indices based on data in xarray.Datasets
+"""
+
+
+def ndvi(scene, red_band="red", nir_band="nir"):
+    """
+    Normalized difference vegetation index
+
+    Calculate the NDVI for the given scene, defined as:
+
+    .. math::
+
+        NDVI = \dfrac{NIR - Red}{NIR + Red}
+
+    Parameters
+    ----------
+    scene : :class:`xarray.Dataset`
+        A Landsat scene, as read with :func:`xlandsat.load_scene`.
+    red_band : str
+        The name of the variable in ``scene`` that corresponds to the red band.
+    nir_band : str
+        The name of the variable in ``scene`` that corresponds to the NIR band.
+
+    Returns
+    -------
+    ndvi : :class:`xarray.DataArray`
+        The calculated NDVI, with the metadata attributes from the original
+        scene.
+    """
+    red = scene[red_band]
+    nir = scene[nir_band]
+    result = (nir - red) / (nir + red)
+    result.name = "ndvi"
+    attrs = {"long_name": "normalized difference vegetation index"}
+    attrs.update(scene.attrs)
+    result = result.assign_attrs(attrs)
+    return result