The paper traces the background, conditions and system study work leading to the development of analytical techniques currently in use for system damping evaluation in England and Wales. The early study work, providing indications of possible low-frequency electromechanical oscillations, is examined together with the early simplified models used for eigenvalue analysis evaluating the damping behaviour of the system during such oscillations. The mechanism producing negative damping of such low frequency electromechanical oscillations is analysed. The development of the detailed eigenvalue analysis program package PRASM currently in use by the CEGB is described in detail. Finally, sample results from the extensive analysis carried out on the CEGB/SSEB oscillation incidents of December 1978-January 1979, utilising the PRASM program package, are given with commentary on likely future developments.