The main focus of the speaker's study has been on the properties of semiconducting materials, determined primarily by use of the transmission electron microscope (TEM), often in conjunction with other advanced analytical methods. The speaker's principal areas of investigation are described briefly: recent key work in the area of epitaxy has involved the mapping of the internal composition of individual quantum dots and the identification of the mechanism of the Stranski-Krastanow epitaxial islanding transition, the latter development providing the solution to an outstanding 60-year mystery.