Irreligion may be defined as the absence of religion, an indifference towards religion, a rejection of religion, or hostility towards religion. When characterized as the rejection of religious belief, it includes atheism and secular humanism. When characterized as hostility towards religion, it includes antitheism, anticlericalism and antireligion. When characterized as indifference to religion, it includes apatheism. When characterized as the absence of religious belief, it may also include agnosticism, ignosticism, nontheism, religious skepticism, and freethought. Irreligion may even include forms of theism depending on the religious context it is defined against, as in 18th century Europe where the epitome of irreligion was deism.

Sixteen percent of the world population (1.1 billion people) are considered non-religious. Some evidence suggests that the fastest growing religious status in the United States is "no religion".

Greg M. Epstein is the current secular humanist chaplain at Harvard University, and is a published author on the subject of secular humanism.

Epstein was born February 4, 1977 and grew up in the ethnically-diverse neighborhood of Flushing, Queens, New York. His parents, though Jewish, were not very religious, and he attended services with them only occasionally, usually during Jewish holidays or festivals. He describes this experience as one of the foundations for his later interest in Humanistic Judaism.

While attending the Stuyvesant High School in Manhattan, Epstein studied Buddhism and Taoism. After graduating from high school, he enrolled in the University of Michigan in Ann Arbor. As part of his undergraduate studies in the University of Michigan's College of Literature, Science, and the Arts, he spent a year in Taiwan in an effort to further his knowledge of Zen Buddhism through readings in Chinese and direct contact with Zen practitioners. Becoming disenchanted with Eastern religions during this experience, Epstein returned to the U.S. and completed his Bachelor of Arts in Religion and Chinese from the University of Michigan. He then went on to complete a Master of Arts in Judaic Studies, also from the University of Michigan.