This book introduces new Monte Carlo methods for computing Value-at-Risk(VAR) in finance. 2 major cases (i.i.d. Monte Carlo and Markov Chain Monte Carlo) are treated in this book. New i.i.d Monte Carlo technique is based on the combination of importance sampling, non-linear optimization, and newly proposed exponential twisting density. Its theoretical justification will also be given based on the Large Deviation Theory and the Laplace method. For the Markov Chain Monte Carlo, this book introduces new techniques based on Metropolis-within-Gibbs algorithm combined with Robbins-Monro algorithm...