Pavel Janak (12 March 1881, Prague - 1 August 1956) was a Czech modernist architect, furniture designer, town planner, professor and theoretician.

Janak studied with Otto Wagner in Vienna between 1906 and 1908, and worked in Prague under Jan Kotera. In 1911, with the publication of an article The Prism and The Pyramid advocating dynamic architectural compositions and destabilizing traditional right-angled building, Janak became the leading theoretician of Czech Cubism. Of the three Czech cubists -Janak, Josef Chochol and Josef Gocar - Janak probably built less and theorized more. Still, his 1913 Fara House in Pelhrimov is a key work in that style.

After 1918 Janak and Gocar developed Cubism into Czech Rondocubism, with decoration taken from folk and nationalist themes, and then subsequently into a purer functionalism. His 1925 Palace Adria is an unusually late example of integrated sculpture. As the chairman of the Czechoslovak Werkbund he drew up the master plan for the 1932 Baba Werkbund Housing Estate, the last of the European housing exhibitions, and also designed 3 of its 32 houses. He was also entrusted with the design for the Hussite Church in Vinohrady.

In 1936 he took over from Joze Plecnik as the supervising architect of Prague Castle.

Pavel Janak was also associated with the functionalist housing project in Prague known as Baba. Baba, was the "Werkbond" inspired housing estate located on the outskirts of Prague. Pavel Janak not only created the Master Plan for this community, he was also in charge of selecting the architects that would be involved. Although Baba survived the destruction of the World Wars, it is in danger of historical extinction due to renovation of new owners with lack of historical reverence and general neglect.