  The fermion bag approach is a new method to tackle fermion sign problems in
lattice field theories. Using this approach it is possible to solve a class of
sign problems that seem unsolvable by traditional methods. The new solutions
emerge when partition functions are written in terms of fermion bags and
bosonic worldlines. In these new variables it is possible to identify hidden
pairing mechanisms which lead to the solutions. The new solutions allow us for
the first time to use Monte Carlo methods to solve a variety of interesting
lattice field theories, thus creating new opportunities for understanding
strongly correlated fermion systems.
