The emission of electrostatic Langmuir waves by collisional process, termed electrostatic bremsstrahlung emission, and the collisional damping of Langmuir waves, which can be considered as the inverse electrostatic bremsstrahlung process, are rigorously discussed. Some inaccuracies in the previous formalisms are also corrected. It is shown that the improved formulae in the case of Maxwellian particle distributions are given in forms where they satisfy Kirchhoff's law in the balanced form.