It is about 10 years since the first published report of laser action at room temperature in a quantum well structure, electrically pumped from a p-n junction(1). Research on the basicproperties of quantum well structures had been in progress pince about 1973, made possible by the developments of molecul4v,beam epitaxy (MBE) 0,3), and later of metalorganic chemical vapour deposition 04011CVD)k4), as techniques for epitaxial growth of thin layers of III-V semiconductors. In his review of 1975 Dingle(5) cited the ability to tune the laser emission wavelength by adjusting the well width, and the fact that the step-like density of states function should modify the gain characteristics compared with the bulk, as attractive features of a quantum well laser. An account,of laser action in such structures, achieved by optical pumping, was published in 19760). It is the purpose of this paper to assess the current capabilities of quantum well lasers, fabricated in the GaAs/AlGaAs materials system, and to review our understanding of their operation. In so doing we adopt a historical view and compare the device performances which have been achieved with the initial expectations, and discuss the reasons for the differences which have emerged. We also review attractive features of QW lasers which have come to light in the course of this research activity. This article falls into three main sections: a brief account of the initial expectations of quantum well lasers, a summary of the performance which has actually been achieved, and an account of our current understanding of the operation of quantum well lasers.