The world is rapidly changing, leading to new societal challenges. At their core, many of these challenges are social, highlighting the need for effective theories of social change. Theories of cultural evolution are perhaps the best candidates for a unifying framework for understanding social change, as they focus on general phenomena of human social life such as cooperation, group structure, and social learning. However, many of these theories were developed to explain pre-industrial or pre-digital societies. I will discuss what it would take to produce theories of cultural evolution that address the complexities and problems of the modern world, highlighting some original work on questions related to social learning, signaling, and intergroup cooperation. I will conclude with a discussion of some of the remaining challenges facing the development of a theoretically strong science of cultural evolution for the 21st century (and beyond).