Lamatto++ is a framework to model mixed-integer nonlinear programming problems especially on (but not limited to) networks. Lamatto++ is completely written in C++ and has interfaces to CPLEX, GUROBI, SCIP and GAMS, where the latter provides access to a large collection of solvers for roughly all kinds of mathematical programming problems. Lamatto++ major features are a unified modeling API and a single interface to all the above mentioned solvers. Lamatto++ comes with extendable data structures to handle graphs and networks and provides automatic unit conversion for physical values. For data I/O and data exchange with third party software, Lamatto++ makes use of the XML parsing library Xerces.