Vasek Pospisil (/ˈvæʃɪk ˈpɒspɪsɪl/ VASH-ik POS-pih-sil; Czech: Vašek Pospíšil, pronounced [ˈvaʃɛk ˈpospiːʃɪl]; born June 23, 1990) is a Canadian former professional tennis player. Pospisil has a career-high singles ranking of world No. 25, and No. 4 in doubles. Along with partner Jack Sock, he won the 2014 Wimbledon Championships and the 2015 Indian Wells Masters men's doubles titles. He also reached the quarterfinals in singles at the 2015 Wimbledon Championships.

Vasek was born on June 23, 1990, in Vernon, British Columbia, to Miloš and Mila. In 1988, before Vasek was born, his parents and older brothers unlawfully drove from Czechoslovakia to Austria to escape the Communist regime. Before moving, Miloš worked as the plant manager of a dairy factory, and Mila taught in a kindergarten. Both had experience playing recreational sports such as tennis with their sons and in local tournaments.

The family lived in northeastern Austria and saved up to move to Canada despite working long hours for low wages. In the summer of 1989, they finally moved to Vernon, British Columbia, a city in the Okanagan Valley, because Miloš's brother was living there after escaping his home country in the years prior. It had a population of only about 38,000. The entire family had a meager understanding of the English language upon their arrival. Miloš worked two jobs, at a flour mill and as a machinery operator at a brewery. He began taking more interest in the game of tennis after the birth of his third son. He coached Vasek's older brothers on community tennis courts, recorded matches on television, and found tips and guidelines in tennis magazines. When Vasek was about 3 years old, he started acting as his brothers' ball boy when they practiced with their father. He also would "drag a mini tennis racquet all over the house."

Vasek played his first tournament at age 6, competing at the under-12 level and still emerging as the champion. Approximately three years later, he participated at the under-9 Little Mo Nationals in San Diego. These victories made Miloš even more enthusiastic about his son's tennis career. As soon as Vasek's brothers reached high school and had played in several tournaments, he was given his first proper lessons. Along with tennis, he also played soccer, basketball, table tennis, and street hockey. Vasek quit soccer when he was only 12 due to injuries and because it got in the way of tennis. He said, "In some ways my heart was broken because I often times had more desire to play soccer than tennis." Pospisil frequently traveled to Kelowna—a 45-minute drive—in the winter so that he could play indoors. He made the trip nearly every day for six consecutive years. In the summer, on the other hand, he had to play with his brothers on the poorly maintained courts of a nearby high school and occasionally took taunts from the students there.

In the fall of 2002, the family had to move to Vancouver so that they could find a tennis coach for their youngest son. They had to leave Miloš behind, as he had to stay in Vernon to work at his brewery, but he would make the four-hour drive on weekends to see them. The decision was also made because Vasek's oldest brother, Tom, was already attending the University of British Columbia (UBC) in Vancouver, and Petr was hoping to start going to the same school. Unlike his siblings, Vasek had been homeschooled since he was 7 years old to prioritize tennis. He said, "I miss my friends a lot [from school] but the home schooling is better. I can do my work almost twice as fast. We thought it would be better to train here. It's a really good club." Vasek was coached by Russian-born Vadim Korkh, who had experience working with players such as Andrei Chesnokov while he was a professor of tennis at the Central Sport Academy in Moscow. Korkh said of Pospisil, "With his dedication and talent there was no question he would succeed. He's a great example for all my students. They all ask about Vasek and I tell them how much dedication he had and I show them his [youth tennis] schedule and they see how hard he worked." Under Korkh, Vasek studied for school and did fitness training as well as practicing tennis. He played with Korkh five days each week, each practice lasting four hours. In November 2002, Vasek went to Florida and won the Prince Cup, defeating several of the best under-12 players from Europe. He also reached the quarterfinals of the Orange Bowl. At the Ellensburg (WA) Open in 2003, Vasek lost a tight 3-setter to Seattle-area phenom Jeffrey Hammond.

Pospisil traveled to play under-14 tournaments in Europe for Tennis Canada in the spring of 2003 with three other players. Being younger than most of the players there, he was quickly defeated by his opponents in the early rounds of the main and consolation draws. He faced a knee injury in the process, something that would trouble him for the 18 months that followed. Pospisil would make the same trip as an older player, but would still see little success. In 2004, he won the Canadian Nationals at the U14 level, securing his spot as the best player in the country for his age group. When Vasek was 14 years old, his father decided to return to coaching his son. Miloš left his brewery, moved to Vancouver, and became Vasek's full-time coach, training him at local high school courts once again.

Initially playing USTA at the age of 7, Vasek won his first 12-and-under tournament. He continued to beat high-ranked and respected players such as Ryan Farber. Pospisil reached the doubles final of his first junior International Tennis Federation event, the 2005 Canadian U18 ITF World Ranking event, with compatriot Graeme Kassautzki. He and Kassautzki won the doubles event. Partnering another star junior Canadian, Milos Raonic, Pospisil won his second doubles title in December 2006, the Prince Cup in the United States. He also won back-to-back doubles titles in the Czech Republic in January and February 2007, as well as the Guru Cup in Italy in May.

In singles, Pospisil won the ITF Flevoland Junior Championships in the Netherlands in February, the 25th All-Canadian ITF Junior Championships in April, and the Canadian U18 ITF World Ranking Event, the last one without losing more than four games in any set.