By Jennifer Mendelsohn

Special Health Report

A ubiquitous topic that no one likes to discuss. A highly private act that catches the public eye. Sublime. Dangerous. Compelling. Confusing. The most fundamental of human experiences, and the one responsible for the perpetuation of our species. Sex.

In recent decades, America's sexual landscape has been rearranged by forces including new forms of contraception, skyrocketing divorce rates, a sea change in women's societal roles and an explosion or graphic media imagery. Even the idea of what constitutes sex - think Bill Clinton and Monica Lewinsky - has changed.

Today, USA WEEKEND Magazine teams up with the Kinsey Institute for Research in Sex, Gender and Reproduction to assess America's sexual health and understanding. The Indiana University-based research institute has created headlines for more than 50 years, ever since biologist Alfred Kinsey published Sexual Behavior in the Human Female - collectively known as the Kinsey reports. These landmark volumes shed the first scientific light on once-taboo topics, such as homosexuality, premarital sex and masturbation. The institute (kinseyinstitute.org) has become the world's foremost repository of information about sex.