Humboldt Research Fellowship for Experienced Researchers

From the program website:

Submit an application if you are a researcher from abroad with above average qualifications, completed your doctorate less than twelve years ago, already have your own research profile and are working at least at the level of Assistant Professor or Junior Research Group Leader or have a record of several years of independent academic work. A Humboldt Research Fellowship for experienced researchers allows you to carry out a long-term research project (6-18 months) you have selected yourself in cooperation with an academic host you have selected yourself at a research institution in Germany. The fellowship is flexible and can be divided up into as many as three stays within three years.

Scientists and scholars of all nationalities and disciplines may apply to the Alexander von Humboldt Foundation directly at any time. The Humboldt Foundation grants approximately 600 Humboldt Research Fellowships for postdoctoral researchers and experienced researchers annually. Short-term study visits, participation in congresses and training courses cannot be financed.

Full application details can be found here: http://www.humboldt-foundation.de/pls/web/docs/F1512/programme_information_e.pdf