Design of composite steel and concrete truss girders is discussed, with an emphasis on longitudinal connection of the steel truss and a concrete slab. While a strongly non-uniform distribution of longitudinal shear due to localized force transfer in truss nodes occurs in elastic stages of early loadings, the plastic redistribution follows up to collapse. The former is of primary interest in the design of bridges, class 3 and 4 cross sections, non-ductile shear connection, and serviceability limit states in general. This research clears up the distribution in elastic phases and the process of plastic redistribution by using data of real bridge structures. Wide parametric studies provide insight into important parameters influencing the distribution, such as rigidities of shear connection, rigidities of steel chord and concrete slab, concentration of shear connectors above truss nodes, influence of temperature effects, shrinkage and creep. Design according to Eurocode 4 is discussed together with common procedures used by designers, referring to rather improper/conservative solutions. The necessity of densification of shear connectors above truss nodes is discussed in detail and suggestions for an iteration analysis for reasonable connection design is proposed.