Grandparents and grandchildren report their relationships with one another are meaningful in many respects, including having the opportunities to exchange affection, receive support, and learn new things from one another. Since 2000, theoretically grounded communication research on grandparent–grandchild (GP–GC) relationships has notably increased. This research has been largely centered in three theoretical domains: research using affection exchange theory (AET), communication accommodation theory (CAT), and communication theory of identity (CTI). AET is a bioevolutionary theory that holds that giving and receiving affectionate communication help facilitate viability and fertility. Consistent with this theory, grandparents have reported better mental health when they express more affectionate communication for their grandchildren, and grandchildren have reported better mental health when they receive more affectionate communication from their grandparents. Researchers can advance the study of GP–GC affectionate communication in the future by examining if affectionate communication is indirectly associated with health outcomes via certain indices of relational solidarity (e.g., shared family identity, relational closeness, perceived availability of social support). CAT is an intergroup and interpersonal communication theory that describes the adjustments speakers make during interaction, as well as the ramifications of those adjustments for receivers. Receivers might interpret a speaker as overaccommodating them (i.e., going too far in the adjustment necessary for appropriate interaction, such as patronizing talk) or underaccommodating them (i.e., not going far enough in the adjustment necessary for appropriate interaction, such as engaging in painful self-disclosures). When grandchildren receive more overaccommodation and underaccommodation from their grandparents, they report more negative prejudicial attitudes toward older adults as a whole. Future researchers should examine how perceptions of accommodation and nonaccommodation in GP–GC relationships are associated with other types of prejudice, such as religious prejudice. Finally, the CTI posits that people hold four frames of identity: personal identity (how people internally view themselves), enacted identity (how people behave or perform their identity), relational identity (how people perceive that their relational partners view them and how people define themselves as in relationships with others), and communal identity (how large social collectives are broadly defined, such as in the mass media). These identity frames can contradict one another, creating identity gaps. Both grandchildren’s and grandparents’ identity gaps (personal-relational and personal-enacted identity gaps) have been indirectly associated with lower intentions on the part of grandchildren to provide care for their grandparents via grandchildren’s reduced communication satisfaction. Future researchers would be well served to examine identity gaps between three or four frames of identity. In sum, many insights have been generated by GP–GC communication research informed by these three theories, and there are numerous ways to continue these lines of research in the future.