Clitic clusters are complex morphological objects that are penetrable by syntactic rules, but behave as (semi)‐autonomous morphosyntactic constituents. Clusters are subject to various kinds of restrictions, which fall into three main types: (i) restrictions on linearization: clitic clusters tend to be rigidly ordered; (ii) restrictions on exponence: certain clitic clusters are morphologically opaque; (iii) restrictions on agreement: clusters of clitic pronouns tend to be ungrammatical when they correspond to certain person/case combinations (the so‐called person case constraint or PCC). Focusing on Romance data, the entry argues that (i) the PCC is part of a wider set of agreement restrictions that do not target only clitics, but become particularly evident when arguments are cliticized; (ii) the PCC is arguably linked to animacy and, more specifically, to the syntactic mechanism whereby animate and non‐animate arguments are licensed in the clause and, consequently, mapped into clitics.