diff --git a/README.md b/README.md
index f2077b42..e0be5362 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ Many datasets are intrinsically hierarchical. Consider [geographic entities](htt
 
 This module implements several popular techniques for visualizing hierarchical data:
 
-**Node-link diagrams** show topology using discrete marks for nodes and links, such as a circle for each node and a line connecting each parent and child. The [“tidy” tree](#tree) is delightfully compact, while the [dendrogram](#cluster) places leaves at the same level. (These have both polar and Cartesian forms.) [Indented trees](https://bl.ocks.org/mbostock/1093025) are useful for interactive browsing.
+**Node-link diagrams** show topology using discrete marks for nodes and links, such as a circle for each node and a line connecting each parent and child. The [“tidy” tree](#tree) is delightfully compact, while the [dendrogram](#cluster) places leaves at the same level. (These have both polar and Cartesian forms.) [Indented trees](https://observablehq.com/@d3/indented-tree) are useful for interactive browsing.
 
 **Adjacency diagrams** show topology through the relative placement of nodes. They may also encode a quantitative dimension in the area of each node, for example to show revenue or file size. The [“icicle” diagram](#partition) uses rectangles, while the “sunburst” uses annular segments.