This is an introduction to the mysterious world of lattice algorithms, which have found many applications in computer science, notably in cryptography. We will explain how lattices are represented by computers. We will present the main hard computational problems on lattices: SVP, CVP and BDD, related to short and close vectors in lattices, and their average version known as SIS and LWE. We will present the celebrated LLL algorithm, Babai’s algorithm and discrete Gaussian sampling. If time allows it, we will also take a look at worst-case to average-case reductions.