The field of active and self-propelled micro- and nanomotors is seeing major advances. It encompasses externally as well as chemically propelled micro- and nanomotors, which are predicted to show fascinating collective phenomena at very high particle fractions. High densities, however, pose challenges for many experimental systems. We have therefore developed appropriate fabrication and assembly schemes that allow us to grow large numbers of catalytically active colloids, based both on inorganic light-induced reactions as well as enzymatic reactions, which can be operated at high densities. This talk will present our latest results and discuss open questions.