This special issue brings together research in multilingualism within applied linguistics to delineate conceptualizations of multilingualism as constructs amenable for classroom and standardized testing systems operations. Specifically, for language testing and assessment, there have been multiple calls for the field to embrace multilingual approaches not only to reflect the full (linguistic) humanity of multilingual peoples but also to contest decades to centuries of marginalization and discrimination against multilingual practices outside monolingual standards. By bringing together and expanding orientations toward multilingualism in content and language assessments, this special issue is positioned to aid with significant shifts in the field of language testing. Separately and together, these papers work to engage with the construct of multilingualism in assessment in ways that point to the complexities and issues that arise. Embracing complexities and the realities they represent for test users serves to create methods and approaches in the field, which is critical for scholarship to keep pace with changes in society and to align with the knowledge base in applied linguistics.