The 2007 Spring Meeting of the Arbeitskreis Festkörperphysik was held in Regensburg, Germany, between March 26 and March 30 2007 in conjunction with the 71st Annual Meeting of the Deutsche Physikalische Gesellschaft. This year's meeting was certainly one of the largest physics meetings in Europe. The present volume 47 of the Advances in Solid State Physics contains the written version of a large number of the invited talks and gives an overview of the present status of solid state physics where low-dimensional systems such as quantum dots and quantum wires are dominating. The importance of magnetic materials and the present day interest into magnetism is reflected by the large number of contributions to the part dealing with ferromagnetic films and particles. One of the most exciting achievements of the last couple of years is the successful application of electrical contacts and the investigation of a single layer of graphene. This exciting physics is covered in Part IV of this book. Terahertz physics is another rapidly moving field which is presented here by five contributions. Achievements in solid state physics are only rarely possible without a thorough knowledge of material physics. Therefore, the last two parts of this book cover material aspects.