For the main part of this dissertation, I have executed a survey of nearby, main sequence A, F, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars to better than 4% accuracy. The results of these observations also yield empirical determinations of stellar linear radii and effective temperatures for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale isochrones to constrain the masses and ages of the stars. These quantities are compared to the results found in Allende Prieto & Lambert (1999), Holmberg et al. (2007), and Takeda (2007), who indirectly determine these same properties by fitting models to observed photometry. I find that for most cases, the models underestimate the radius of the star by ~12%, while in turn they overestimate the effective temperature by ~ 1.5 - 4%, when compared to my directly measured values, with no apparent correlation to the star's metallicity or color index. These overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than ~ 1.3 M_sol. Alternatively, these quantities I measure are also compared to direct measurements from a large sample of eclipsing binary stars in Andersen (1991), and excellent agreement is seen within both data sets. Finally, a multi-parameter solution is found to fit color-temperature-metallicity values of the stars in this sample to provide a new calibration of the effective temperature scale for these types of stars. Published work in the field of stellar interferometry and optical spectroscopy of early-type stars are presented in Appendix D and E, respectively.

Context: Binaries and multiple systems are very frequent and form large fraction of all stellar systems. In contrast to their single counterparts, studying binaries provides the possibility to accurately determine fundamental properties of their components that are needed for testing models of stellar structure and evolution. On top of that, binaries can be used for accurate distance determinations. The mass exchange in close binaries remains the only mechanism, which completely alters their evolution. Aims: The primary goal of my doctoral study was to determine orbital elements of selected systems and properties of their components - masses, radii, and ef- fective temperatures. - In case of more complicated objects (e.g. interacting multiple systems, mass-transferring binaries, . . . ) the secondary goal was to confront our results with predictions of theoretical models. Methods: Studies that I co-authored were based on three different types of ob- servations, each sensitive to partly different properties of studied systems - photometry, spectroscopy, and spectro-interferometry. The analysis was carried out through several "observation-specific" models, whose outcome was critically compared to each other and to previous studies of the object in question. Results: Throughout my study I contributed to: (i)...