Leonard Knyff or Leendert Knijff was a Dutch draughtsman and painter. He was the son of landscape painter Wouter Knijff and the brother of Jacob Knijff and left around 1681 from Holland to England. Knyff collaborated with Kip to produce views of country houses and gardens for Britannia Illustrata and Le Nouveau Théâtre.

The topographical images of Kip and Knyff are significant for providing reliable illustrations of the development of the formal English garden in the Dutch-French style. Their documentary information for this period in British architecture and landscape design is particularly valued because, within a generation, the formal gardens seen in these views would be swept away in favor of the pastoral compositions, derived from idealized landscapes of painters such as Claude Lorrain, that characterize the "naturalistic" English landscape gardens.

In the later 20th century many of the Kip and Knyff views were hand-coloured, as monochrome landscapes proved increasingly harder to sell in the market.

He was born in Haarlem as the son of the painter Wouter Knijff, where he received his training as an artist. He moved to London around 1681 and though he returned to the Netherlands on trips, he stayed in London until he died. He is known for paintings, drawings, and art auctions. He collaborated with Jan Kip on a series of engravings of English country houses.

His brother Jacob Knijff was a marine painter.