The volume Null Objects from a Cross-Linguistic and Developmental Perspective brings together theoretical and empirical contributions on missing object constructions, revealing a nuanced and multifaceted phenomenon that poses challenges to current theories of null objects. The selected papers highlight the significance of the interplay between formal constraints and semantic properties (namely definiteness and animacy) in the licensing of null objects cross-linguistically. The formally oriented papers contribute to ongoing discussions on the mechanisms underlying the derivation of null objects. The differences between null objects that are licensed by rich agreement and those that are agreement independent are also addressed. From a developmental perspective, the papers on null objects in language acquisition, including second language learning, further provide valuable insights into the intricate processes underlying the acquisition of referential expressions. The role of animacy emerges as a central question, particularly in the context of Portuguese varieties, where differences in pronominal systems contribute to variation in null object distribution.