The study of operator algebras on Hilbert spaces, and C*-algebras in particular, is one of the most active areas within Functional Analysis. A natural generalization of these is to replace Hilbert spaces (which are $L^2$-spaces) with $L^p$-spaces, for $p\in [1,\infty)$... The study of such algebras of operators is notoriously more challenging, due to the lack of orthogonality in $L^p$-spaces. We give a modern overview of a research area whose beginnings can be traced back to the 50's, and that has seen renewed attention in the last decade through the infusion of new techniques. The combination of these new ideas with old tools was the key to answer some long standing questions. Among others, we provide a description of all unital contractive homomorphisms between algebras of $p$-pseudofunctions of groups. (read more)