Ubiquitin (Ub) and ubiquitin-like (Ubl) proteins are activated and conjugated to substrates in response to various stimuli, but all depend on the coordinated action of E1 activating enzymes, E2 conjugating proteins and E3 protein ligases to ensure conjugation to a particular target. Efforts are focused on reconstituting complexes in this process to determine how their architectures contribute to specificity during transfer between E1, E2 and E3s, a process that ultimately leads to substrate conjugation. This presentation will include discussion of ongoing work that details mechanisms required for Ub/Ubl conjugation and recognition using chemical approaches and through characterization of complexes isolated within the conjugation cascade.