The 34th Annual Conference on Learning Theory (COLT 2021) will take place August 15-19, 2021. Assuming the circumstances allow for an in-person conference it will be held at CU Boulder, in Colorado. We invite submissions of papers addressing theoretical aspects of machine learning, broadly defined as a subject at the intersection of computer science, statistics and applied mathematics. We strongly support an inclusive view of learning theory, including fundamental theoretical aspects of learnability in various contexts, and theory that sheds light on empirical phenomena.