Baer’s theorem is one of the cornerstone result in group theory, providing critical insights into the relationship between the finiteness of central factor group and that of the commutator sub- group. Building upon Schur’s foundational work, Baer’s theorem connects the upper and lower central series, establishing constraints on group structure that have far-reaching implications. This paper pro- vides a brief review of Baer’s theorem, detailing its historical development, generalizations, and recent extensions. Some key results include exponents, bounds on central series, extensions to locally gen- eralized radical groups, finite rank conditions and applications to automorphism-influenced properties are given. Invoking the notion of variety of groups, we also propound the Baer’s (or Schur’s) theorem in its most general form as a fundamental question and attempt to identify all classes of groups that are Schur-Baer with respect to some variety as potential answers. Particular attention is also given to some of its applications in diverse areas of mathematics. Furthermore, the paper explores open problems and potential research directions, underscoring the theorem’s enduring significance and its role in shaping contemporary mathematical inquiry.

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