Methods for calculating the pressure distribution on a two-dimensional aerofoil in attached viscous transonic flow have been developed at the RAE, Farnborough, a summary of that work (up to 1975) being referenced. Two methods are now established. They are extensions that take account of the boundary layer and wake to two inviscid transonic flow methods: that of Garabedian and Korn (G&K) and a solution to the Transonic Small Perturbation (TSP) equation. Wind-tunnel constraint terms have been incorporated into the viscous version of the TSP method and this form has been the subject of an extensive evaluation performed by comparison with uncorrected experimental data. The evaluation also includes comparisons between the two methods in free-air conditions. A summary of the inviscid methods (G&K and TSP) is given as well as some brief details of the application of tunnel constraint terms. The methods of allowing for viscous effects are also outlined. Details of the viscous flow computer programs (VGK and VISTRAN) are given and a comment is made on the different procedures used to calculate drag coefficient. A summary of the evaluation of the methods is presented and a few typical examples are given. Finally, conclusions including recommendations regarding the method to be preferred are provided.