Abstract: Galaxies are not distributed at random. Rather, they are highly clustered, following closely the distribution of dark matter on large scales and depending strongly on the physical properties of galaxies. Studies of the clustering as a function of galaxy properties should in principle provide interesting constraints on the physical link between galaxies and their host dark matter halos. Indeed, this has been one of the key goals of the many large redshift surveys of galaxies accomplished so far. In this talk I will focus on the clustering of active galactic nuclei (AGN) in the Sloan Digital Sky Survey (SDSS) on a wide range of spatial scales from the regime of galaxy-galaxy interactions up to the linear regime. We studied both optically-identified narrow-line AGN and radio-loud AGN falling in the SDSS footprint. Through constructing halo-based models we're able to estimate the dark matter halo mass, and constrain the local environment where AGN are preferentially found. I will also discuss the implications of the clustering measurements on the AGN unification model.