"What is Liberalism?" is an English adaptation by Conde B. Pallen, Ph.D., of the original Spanish work by Dr. Don Felix Sarda y Salvany. This book critically examines the ideology of liberalism from a Catholic perspective. Dr. Sarda y Salvany argues that liberalism, with its emphasis on individual freedom and secularism, poses a significant threat to the principles and doctrines of the Catholic Church. The text delves into the philosophical and moral underpinnings of liberal thought, highlighting its perceived contradictions and adverse effects on society and religion. The author contends that true liberty is found within the framework of Christian teachings and that liberalism undermines this by promoting moral relativism and weakening religious authority.