Research interests on intermetallic gamma-TiAl based alloys have been increasing over the last decades. Gamma-TiAl alloys are structure materials that can be applied up to service temperatures of 800°C. Due to their low density of about 4 g/cm3 and their high specific strength they are promising candidates for high temperature applications in aeroengines and the automotive industry. Apart from their excellent high temperature properties TiAl alloys are very brittle at room temperature. The characterization of a recently developed TiAl alloy (TNM alloy) containing Nb, Mo and B was the task of the present work. This alloy exhibits appropriate mechanical properties as well as good workability at elevated temperatures and can be forged at near conventional conditions. Quantitative metallographic analyses were conducted to describe the appearing phases and their dependence on temperature. To study the evolution of the microstructure more thoroughly, electron backscatter diffraction (EBSD) measurements were conducted on samples which show different stages of cellular reaction. For the determination of phase transformation temperatures and ordering temperatures within the alloy both synchrotron and neutron diffraction experiments were performed. A model of the lamellae formation based on TEM- and XRD-measurements is proposed which gives a connection between microstructure and mechanical properties of the multiphase material.