The Fourth International Conference on Topological Algebras and Their Applications was held in Oaxaca, Mexico. This meeting brought together international specialists and Mexican specialists in topological algebras, locally convex and Banach spaces, spectral theory, and operator theory and related topics. This volume contains talks presented at the conference as well as articles received in response to a call for papers; some are expository and provide new insights, while others contain new research. The book is suitable for graduate students and research mathematicians working in topological vector spaces, topological algebras, and their applications.