This volume presents an overview of the techniques of quasilinearization as they are applied to the problem of system identification. The quasilinear technique has inherent advantages in establishing the intricate interrelationships which exist in complex physical systems. Several advanced topics which are central to the quasilinear technique are discussed in this book. Problems on orbit determination, estimation of chemical rate constants, complex biomechanics of systems and analytical medicine are investigated, to demonstrate the power of the quasilinear method. The reader will have a good idea of the wide range and complexity of problems which can be solved.