---
abstract: |
    I review here past and present research on clusters and groups of galaxies within the Sloan Digital Sky Survey (SDSS). I begin with a short review of the SDSS and efforts to find clusters of galaxies using both the photometric and spectroscopic SDSS data. In particular, I discuss the C4 algorithm which is designed to search for clusters and groups within a 7–dimensional data–space, [*i.e.*]{}, simultaneous clustering in both color and space. Also, the C4 catalog has a well quantified selection function based on mock SDSS galaxy catalogs constructed from the Hubble Volume simulation. The C4 catalog is $>90\%$ complete, with $<10\%$ contamination, for halos of ${\rm
    M_{200}} > 10^{14}{\rm M_{\odot}}$ at $z<0.14$. Furthermore, the observed summed $r$-band luminosity of C4 clusters is linearly related to ${\rm M_{200}}$ with $<30\%$ scatter at any given halo mass. I also briefly review the selection and observation of Luminous Red Galaxies (LRGs) and demonstrate that these galaxies have a similar clustering strength as clusters and groups of galaxies. I outline a new collaboration planning to obtain redshifts for 10,000 LRGs at $0.4<z<0.7$ using the SDSS photometric data and the AAT 2dF instrument. Finally, I review the role of clusters and 