In casual situations, sure, people use the words interchangeably. But there are certain situations when one is more appropriate. Example: "Sex" is determined biologically by what sex chromosomes you inherit. You are male if you have a Y chromosome. You are female if you do not have a Y chromosome. Generally, males have one X and one Y chromosome in their genome, and females have two X chromosomes. Certain abnormalities can occur that result in individuals with XXY, XO (just an X), XXX, and XYY sex chromosomes, but even then, their biological sex is determined by the presence or absence of a Y chromosome. On the other hand, "gender" refers to sociocultural and psychological roles individuals have as a result of their classification as a male, a female, or something else entirely. Over the years, as American society has become more comfortable with discussing gender issues, many interesting observations and assertions have arisen. For example: 1. Women's suffrage (the right to vote) was won at the turn of the last century because many people (both men and women) felt that all citizens, regardless of gender, had the right to participate in government. 2. Paternity leave (the equivalent of maternity leave) is offered by more and more companies, as men today discover that they too can juggle family and work, just as women have been doing for centuries. 3. Many people assert that there is more to the gender debate than we all previously thought. They explain that it's not accurate to categorize all individuals into distinct categories such as heterosexual, gay, lesbian, bisexual, transgender, and transsexual anymore. Research is being advocated that will study whether a gender identity and sexual orientation could be described as a spectrum of possibilities rather than strict categories, and whether one's gender identity and/or sexual orientation can change over time, even from day to day. Hope that helps.