In many ways, our immune systems are as complex as our brains. They learn, predict, remember and adapt, protecting us from the maelstrom of pathogens that infect us daily. Computer Science frequently takes inspiration from the seemingly endless capabilities of natural systems. It should therefore be no s- prise that, like the field of Artificial Neural Networks inspired from brains, we now have a vigorous field of research known as Artificial Immune Systems (AIS), inspired by our own immune systems. Although still relatively new, the previous 10 years has seen the paradigm of AIS rapidly establish itself as an important biological metaphor. Researchers all over the world fruitfully exploit “immunological ideas” in many different ways to provide mechanisms for tackling a wide variety of applications. In this volume we present the proceedings of ICARIS 2003, the 2nd Int- national Conference on Artificial Immune Systems. This was the second int- national conference entirely dedicated to the field, and followed the extremely successful first conference held in Canterbury, UK in 2002. The number and - versity of papers in this year’s conference is atribute to the ever-growing number of researchers in the area, and representative of the solid foundation of work that now exists in this area. The range of topics considered is wide. For example, at one end of the spectrum we see a selection of papers providing a necessary t- oretical grounding for the field. At the other end, we have an exciting range of applications to real-world problems, covering, for example, job-shop scheduling and fault detection in refrigeration systems.