A ubiquitous feature of cold dark matter paradigm is emergence of dark matter clusters (or haloes) on a large range of scales. Observational studies of these clusters can teach us a wealth of information, ranging from cosmology to particle physics. I first talk about largest of these clusters, and how they can teach us about cosmology. In particular, I will discuss how well linear growth of density perturbations can be tied to cluster number counts. I will then turn to dark matter clustering on small scales, and introduce a novel analytic framework to predict its properties. This leads to interesting signatures in dark matter direct and indirect detection experiments, and even pulsar timing observations.