Focusing on the mathematics that lies at the intersection of probability theory, statistical physics, combinatorics and computer science, this volume collects together lecture notes on recent developments in the area. The common ground of these subjects is perhaps best described by the three terms in the title: Random Walks, Random Fields and Disordered Systems. The specific topics covered include a study of Branching Brownian Motion from the perspective of disordered (spin-glass) systems, a detailed analysis of weakly self-avoiding random walks in four spatial dimensions via methods of field theory and the renormalization group, a study of phase transitions in disordered discrete structures using a rigorous version of the cavity method, a survey of recent work on interacting polymers in the ballisticity regime and, finally, a treatise on two-dimensional loop-soup models and their connection to conformally invariant systems and the Gaussian Free Field. The notes are aimed at early graduate students with a modest background in probability and mathematical physics, although they could also be enjoyed by seasoned researchers interested in learning about recent advances in the above fields.

The Lecture Notes collect seven mini-courses presented at the 5th Prague Summer School on Mathematical Statistical Physics that took placeduringtwoweeksofSeptember2006.Aswithprecedingschools, it was aimed at PhD students and young postdocs. The central theme of the volume is what could be called "mathematics of phase transitions" in diverse contexts. Even though all courses were meant to introduce the reader to recent progress of a particular topic of modern statis- cal physics, attention has been paid to providing a solid grounding by carefully developing various basic tools. One of the techniques that led, more than two decades ago, to a seriesofimportantoutcomesinthetheoryofphasetransitionsoflattice models was re?ection positivity. Recently it resurfaced and was used to obtain interesting new results in various settings. The lectures of Marek Biskup include a thorough introduction to re?ection positivity as well as a review of its recent applications. In addition, it contains a crash course on lattice spin models that is useful as a background for other lectures of the collection. Also the following two contributions concern equilibrium statistical physics.ThelecturesofDmitriIo?earedevotedtoastochasticgeom- ricreformulationofclassicalaswellasquantumIsingmodels.Auni?ed approachtotheFortuin-Kasteleynandrandomcurrentrepresentations in terms of path integrals is presented. Statistical mechanics of directed polymers interacting with o- dimensionalspatiale?ectsisatopicwithvariousapplicationsinphysics and biophysics. The lectures of Fabio Toninelli are devoted to a th- ough discussion of the localization/delocalization transition in these models.