The Guest Program is the key concept distinguishing the Max Planck Institute for Mathematics from other Max Planck Institutes. Within the program mathematicians with a completed Ph.D. can work at the MPIM for a fixed period of time, ranging from weeks to several months. Young researches at the postdoctoral level can get in contact to established scientists, who enjoy staying at the MPIM for a sabbatical. The whole concept of the program is about stimulating the communication and the exchange of ideas within the mathematics community. Over the years a few thousand mathematicians have used this unique opportunity.