Although most people remain unaware of its presence in the background, the ever-increasing complexity of IT, with its multiple sources, has been an ongoing issue for quite some time. It can even be qualified as a crisis, in both hardware and software. Indeed, this complexity has reached the point where systems are no longer fully understandable by human beings, which raises the question of how we can continue being in full control of their functioning. It is of course a matter of cost for the IT industry. But a number of incidents caused by bugs or a misunderstanding of some part of an IT system have already occurred. With an IT world that is permanently connected on a worldwide scale, the risk of damage caused by the lack of control of IT systems is both real and growing, with errors and malevolent attacks the most likely culprits. Taming the IT complexity hydra is thus more necessary than ever. Fortunately, various solutions can be proposed to tackle the various heads of the hydra (i.e. the various aspects of complexity); these are solutions based on existing methodologies, tools and resources or extensions thereof.