As an expert in quantum computation and its applications, the focus of Ignacio Ciracs research is the quantum theory of information. With his colleague Peter Zoller, he has made the first proposals to build quantum computers and quantum simulators using ions, neutral atoms, and other physical systems. He also discovered how cold atoms experiments can be used to solve problems in material science, high-energy physics, and quantum chemistry. He developed several quantum algorithms to solve a variety of problems with quantum computers. In the field of quantum communication, he introduced the concept of quantum repeaters, proposed the first ways of implementing them with atoms and photons, and provided the first security proof for continuous variable quantum cryptography. He has also introduced basic concepts and techniques in quantum information theory and, in particular, in entanglement theory. With several collaborators, he introduced projected entangled-pair states, which are now widely used in classical computational physics. Additionally, he developed a theory of tensor networks, and related the entanglement in a many-body quantum system with the possibility of describing it efficiently.