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".

Peter John Kreeft (born 1937) is a professor of philosophy at Boston College and The King's College. He is the author of numerous books as well as a popular writer of Christian philosophy, theology and apologetics. He also formulated, together with Ronald K. Tacelli, SJ, "Twenty Arguments for the Existence of God".

Kreeft took his A.B. at Calvin College (1959), and an M.A. at Fordham University (1961). In the same university he completed his doctoral studies in 1965. He briefly did post graduate studies at Yale University.

Kreeft has received several honors for achievements in philosophical reasoning. They include the following: Woodrow Wilson, Yale-Sterling Fellowship, Newman Alumni Scholarship, Danforth Asian Religions Fellowship, and Weathersfield Homeland Foundation Fellowship.

He joined the Philosophy faculty of the Department of Philosophy of Boston College in 1965. His intellectual reputation stems from his strengths in debating and summarizing the philosophical arguments of the major Western philosophers. He has debated several academics in issues related to God's existence. Shortly after he began teaching at Boston College he was challenged to a debate on the existence of God between himself and Paul Breines, an atheist history professor, which was attended by a majority of undergraduate students. Kreeft later used many of the arguments in this debate to create the Handbook of Christian Apologetics with then undergraduate student Ronald K. Tacelli, S.J..

Darrel Wayne Ray (born 1950) is a writer and speaker on leadership and organizational development and author of two books on the topic. He is the author of the book The God Virus: How Religion Affects Our Lives and Culture. Ray is founder of the organization "Recovering Religionists", a national self-help group for those leaving their religious indoctrination. In May 2011, he published the survey Sex and Secularism: What Happens When You Leave Religion?.

Ray was raised a fundamentalist Christian in Wichita, Kansas by parents who eventually became missionaries, and among family members highly involved in church life.

In 1972, he earned a bachelor's degree in sociology/anthropology at Friends University in Wichita, Kansas, and in 1974 he completed an MA in Church and Community at Scarritt College for Christian Workers in Nashville, Tennessee. In 1978 he finished a doctoral program in psychology at Peabody College of Vanderbilt University, earning his Ed.D.

In 1979, Ray joined the Quaker church and later he attended the Presbyterian church. From 1969 to 1984 he taught Sunday school, preached, and was a tenor soloist in several church choirs. He left the church in the mid 1980s.