Primordial perturbations from inflation

I review the standard analysis of adiabatic scalar and tensor perturbations produced by slow-roll inflation driven by a single scalar field, before going on to discuss recent work on the role of non-adiabatic modes during and after inflation. Isocurvature perturbations correlated with adiabatic modes may be produced during multi-field inflation and would give valuable information about the physics of the early universe. A significant contribution from correlated isocurvature perturbations is not ruled out by present data, but should be either detected or ruled out by future observations.