100 Years of Brownian motion
  In the year 1905 Albert Einstein published four papers that raised him to a giant in the history of science of all times. These works encompass the photon hypothesis (for which he obtained the Nobel prize in 1921), his first two papers on (special) relativity theory and, of course, his first paper on Brownian motion, entitled "\"Uber die von der molekularkinetischen Theorie der W\"arme geforderte Bewegung von in ruhenden Fl\"ussigkeiten suspendierten Teilchen'' (submitted on May 11, 1905). Thanks to Einstein intuition, the phenomenon observed by the Scottish botanist Rober Brown in 1827 - a little more than a naturalist's curiosity - becomes the keystone of a fully probabilistic formulation of statistical mechanics and a well-established subject of physical investigation which we celebrate in this Focus issue entitled - for this reason - : ``100 Years of Brownian Motion''. 
Peter H\"anggi and Fabio Marchesoni