The lecture will help to understand how the concepts of occultism and esotericism were formed - from ancient traditions to the mass culture of the 20th and 21st centuries. Occult and esoteric teachings often find themselves in the realm of curiosity, anxiety, and debate. Some see them as a cultural phenomenon, others as a set of dangerous misconceptions, while others try to understand why such ideas repeatedly become popular in different historical eras. Listeners will learn how the definitions of occultism and esotericism were shaped, what traditions influenced Western esotericism from antiquity to the 19th century, and why the 19th century became a time of renewed interest in secret knowledge, mystical practices, and unusual spiritual quests. A separate section will be dedicated to how these ideas transformed in the 20th and 21st centuries, moved beyond narrow circles, and became part of mass culture, public discussions, and everyday informational noise.