The Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act is a landmark United States federal law, passed on October 22, 2009, and signed into law by President Barack Obama on October 28, 2009, as a rider to the National Defense Authorization Act for 2010 (H.R. 2647). Conceived as a response to the murders of Matthew Shepard and James Byrd Jr., both in 1998, the measure expands the 1968 United States federal hate-crime law to include crimes motivated by a victim's actual or perceived gender, sexual orientation, gender identity, or disability.

The bill also:

The Act is named after Matthew Shepard and James Byrd Jr. Shepard was a student who was tortured and murdered in 1998 near Laramie, Wyoming. The attack was widely reported due to him being gay, and the trial employed a gay panic defense. Byrd was an African American man who was tied to a truck by two white supremacists and a third man who had no racist background, dragged behind it, and decapitated in Jasper, Texas, in 1998. Shepard's murderers were given life sentences—in large part because his parents sought mercy for his killers. Two of Byrd's murderers were sentenced to death and executed in 2011 and 2019, respectively, while the third was sentenced to life in prison. All the convictions were obtained without the assistance of hate crimes laws, since none were applicable at the time.

The murders and subsequent trials brought national and international attention to the desire to amend U.S. hate crime legislation at both the state and federal levels. Wyoming hate crime laws at the time did not recognize homosexuals as a suspect class, whereas Texas had no hate crime laws at all.

Supporters of an expansion of hate crime laws argued that hate crimes are worse than regular crimes without a prejudiced motivation from a psychological perspective. The time it takes to mentally recover from a hate crime is almost twice as long as it is for a regular crime, and LGBTQ people often feel as if they are being punished for their sexuality, which leads to higher incidence of depression, anxiety, and post-traumatic stress disorder. They also cited the response to Shepard's murder by many LGBT people, especially youth, who reported going back into the closet, fearing for their safety, experiencing a strong sense of self-loathing, and upset that the same thing could happen to them because of their sexual orientation.

The 1968 federal hate-crime law (18 U.S.C. § 245(b)(2)) extends to crimes motivated by actual or perceived race, color, religion, or national origin, and only while the victim is engaging in a federally protected activity, like voting or going to school. Penalties, under both the existing law and the LLEHCPA (Local Law Enforcement Hate Crimes Prevention Act, originally called the "Local Law Enforcement Enhancement Act"), for hate crimes involving firearms are prison terms of up to 10 years, while crimes involving kidnapping, sexual assault, or murder can bring life in prison. In 1990, Congress passed the Hate Crimes Statistics Act which allowed the government to count the incidence of hate crimes based on religion, race, national origin, and sexual orientation. However, a sentence was added onto the end of bill stating that federal funds should not be used to "promote or encourage homosexuality".

According to FBI statistics, of the over 113,000 hate crimes since 1991, 55% were motivated by racial bias, 17% by religious bias, 14% sexual orientation bias, 14% ethnicity bias, and 1% disability bias.

Although not necessarily on the same scale as Matthew Shepard's murder, violent incidences against gays and lesbians occur frequently. Gay and lesbian people are often verbally abused, assaulted both physically and sexually, and threatened not just by peers and strangers, but also by family members. One study of 192 gay men aged 14–21 found that approximately 1/3 reported being verbally assaulted by at least one family member when they came out and another 10% reported being physically assaulted. Gay and lesbian youth are particularly prone to victimization. A nationwide study of over 9,000 gay high school students revealed that 24% of gay men and 11% of gay women reported being victimized at least ten times a year due to their sexual orientation. Victims often experience severe depression, a sense of helplessness, low self-esteem, and frequent suicidal thoughts. Gay youth are two to four times more likely to be threatened with a deadly weapon at school and miss more days of school than their heterosexual peers. Further, they are two to seven times more likely to attempt suicide. Some feel these issues, the societal stigma around homosexuality and fear of bias-motivated attack, lead to gay men and women, especially teenagers, becoming more likely to abuse drugs such as marijuana and cocaine and alcohol, have unprotected sex with multiple sexual partners, find themselves in unwanted sexual situations, have body image and eating disorders, and be at higher risk for STDs and HIV/AIDS.