The course will present an introduction to the theory of determinantal point processes (DPP) and its use for the solution to the problem of the length of the longest increasing sub- sequence in a large random permutation. A celebrated result, belonging to what is now called ”integrable probability” and first proved by Baik-Deift-Johansson in 1999, asserts that the fluctuation of this length around its average is asymptotically distributed according to the Tracy-Widom distribution, similarly to the largest eigenvalue of a random Hermitian Gauss- ian matrix.