Born out of wedlock, Leonardo initially lived with his mother, Caterina. He was later brought into his father, Piero da Vinci's household. He developed relationships with his paternal grandparents and stepmothers. Details about his early childhood relationships are scarce, but they undoubtedly shaped his personality.

His apprenticeship with Verrocchio would have involved a close relationship with the master and fellow apprentices such as Lorenzo di Credi. These relationships shaped his artistic development and provided a social context within the workshop.

Leonardo, along with others, was anonymously accused of sodomy. The charges were dropped due to lack of evidence. While the truth of the accusation remains unknown, this event likely impacted Leonardo's life and potentially his relationships.

Serving as the court artist and engineer for Ludovico Sforza, Leonardo developed a professional relationship with the Duke of Milan. This relationship, although primarily professional, provided Leonardo with patronage and opportunities for artistic and scientific endeavors. Sforza's protection was crucial for his work.

Leonardo had several pupils and assistants throughout his life, including Salaì (Gian Giacomo Caprotti) and Francesco Melzi. These relationships were complex, often involving mentorship, collaboration, and even familial affection. Salaì, in particular, lived with Leonardo for many years and was a constant presence in his life, although their relationship was sometimes turbulent.

Leonardo was invited to France by King Francis I, who admired his genius and provided him with a comfortable residence and generous patronage. This relationship afforded Leonardo the freedom to continue his studies and artistic pursuits in his final years. Francis I treated Leonardo with great respect.

Leonardo da Vinci's wills provide an understanding of his relationship with Salaì and other assistants. They indicate he passed on paintings, personal items and land to them.