Stellar Clusters
Lecture notes by Professor Barbara Ryden.
http://www-astronomy.mps.ohio-state.edu/~ryden/ast162_4/notes17.html

Star Clusters
General information on star clusters from SEDS.
http://www.seds.org/messier/cluster.html

Lacaille and his catalog of clusters and nebulae
A discussion of Lacaille's catalog, which is mainly of historical interest. Includes the catalog itself.
http://bozo.lpl.arizona.edu/messier/xtra/history/lacaille.html