reviewed by several speakers, including Simon White, Alan Dressler, Gus Oemler and Guinevere Kauffmann. Therefore, I will not dwell on justifying the importance of clusters to cosmological research, but simply direct the reader to the reviews by these authors.

Instead, I provide below a brief overview of the Sloan Digital Sky Survey (SDSS), followed by a discussion of the cluster–finding algorithms (Section \[algorithms\]) used within the SDSS collaboration and present new scientific results obtained from studies of galaxies as a function of environment (Section \[environ\]).

### The Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS; York et al. 2000; Stoughton et al. 2002) is a joint multi–color ($u,g,r,i,z$) imaging and medium resolution (R=1800; 3700$\aa$ to 9100$\aa$) spectroscopic survey of the northern hemisphere using a dedicated 2.5 meter telescope located at the Apache Point Observatory near Sunspot in New Mexico. During well–defined (seeing $<1.7''$) photometric conditions, the SDSS employs a mosaic camera of 54 CCD chips to image the sky via the drift-scanning technique (see Gunn et al. 1998). These data are reduced at Fermilab using a dedicated photometric analysis pipeline (PHOTO; see Lupton et al. 2001) and object catalogs obtained for spectroscopic target selection. During non–photometric conditions, the 