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Cooperatively shared wide-area omputing platforms, su h as PlanetLab, provide a large pool of geographi ally distributed resour es whi h an be utilized for building highly available and s alable servi es. In this thesis, we present me hanisms and models for building autonomi ally s alable and resilient servi es on su h platforms. In su h platforms resour es at a node are allo ated to ompeting users on fair-share basis, without any reserved resour e apa ities for any user. There is no platform-wide resour e manager for the pla ement of users on di erent nodes. The users independently sele t nodes for their appli ations. Moreover, a node an be ome unavailable at any time due to rashes or shutdown. Our fo us is on the PlanetLab platform whi h exempli es the platform level hara teristi s onsidered here. Building s alable servi es in su h environments poses unique hallenges due to u tuations in the available resour e apa ities and node rashes. The servi e load may surge in a short time due to ash rowds. We present here models for estimating the servi e apa ity under varying operating onditions. Autonomi s aling of servi e apa ity is performed by dynami ontrol of the degree of servi e repli ation based on the estimated servi e apa ity and the observed load. This requires sele tion of appropriate nodes for the pla ement of new repli as. Furthermore adaptive load distribution me hanisms are needed be ause of the varying servi e apa ities of the individual repli as. We present the experimental evaluations of these me hanisms on PlanetLab. i