When a child is born, a doctor says, "It's a boy" or "It's a girl."

Assigning someone's sex is based on biology -- chromosomes, anatomy, and hormones. But a person's gender identity -- the inner sense of being male, female, or both -- doesn't always match their biology. Transgender people say they were assigned a sex that isn't true to who they are.

Many people have assumptions about what it means to be transgender, but it isn't about surgery, or sexual orientation, or even how someone dresses. It's how they feel inside.

The Williams Institute says there are nearly 700,000 people living publicly as transgender in the U.S. Each one is unique, and their journeys are personal. Some say they are the opposite sex of what they were assigned at birth. Some feel they are both male and female. Still others don't identify as either gender.

"It takes a lot of courage to buck the culture's norm that gender is binary," says Helen R. Friedman, PhD, a clinical psychologist in St. Louis who specializes in gender identity and transgender issues. "The truth is, gender does exist on a continuum." Meaning, there's a lot of in-between.