The possible use of the Very Long Amplitude Interferometer in several programs of astrometric measurements and observations will be described. These programs include short-arc or differential astrometry, large-arc astrometry for zonal corrections in the FK-4 datalog and absolute astrometry primarily for the study of earth rotation. The basic techniques for these different applications, the relevant measurement precision and accuracy, and the related signal-to-noise ratios will be discussed. The role of the atmosphere and the critical atmospheric parameters, as they relate to the astrometric measurements, will be discussed including the atmospheric delay correction by the use of two separate wavelengths. The role of various types of ground motion i.e. seismic disturbance for the different types of astrometry will be discussed and data presented as to the possible effects. Measurements on the stability of equipment will also be included. In addition the use of a two color refractometer for site surveys and the evaluation of gravity waves in the atmosphere will be considered. The procedure for references to the vertical (which is required for earth rotation) will be considered.

Michelson,one-dimensional, and two-dimensional apertures are used to obtain the statistical properties of the solar granulation. The calibration of the power spectrum is performed via Michelson stellar interferometry as well as by the use of changes in seeing conditions during speckle-interferometric measurements. The correction of 40 analyses, determined with Fried's parameter ro ranging between 2.5 cm and 11.5 cm, provides satisfactory convergence for frequencies up to 3 cycles per arc second

This review of the lunar occultation technique summarizes results of 94 diameter measurements for 62 stars. The range of angular diameters measured, the coverage of spectral types, and the wavelengths studied are illustrated and discussedo Comparison with other techniques, magnitude limits and possible future developments are also considered.

The angular diameters ad shapes of bright infrared stars are now being measured from 2 micron to 20 microns using several newly developed techniques of high angular resolution interferometry. These objects possess circumstellar shells emitting in the temperature range 300-600K, thus the brightest of their number have sizes ranging from 0 1 to 10 arcseconds, and are readily resolved by instruments a few meters across.

The size, shape, and structure of several typesof stars will be discussed in detail as the Colloquium proceeds. It will be seen that this information can be used to help characterize the optical properties of the particulate material contained in the circumstellar envelopes. Conclusions concerning the formation and evolution of these cold outer regions of stars may also be possible It appears that the conditions in some of these circumstellar envelopes may be suitable for the formation of planets, a process which may be studied directly as these new techniques are further developed.

Although sensitivities of present instruments are still somewhat marginal, it is now possible to resolve the brightest of the extragalactic nuclei at 10 microns Future instrumental developments should bring the size and structure of many extragalactic nuclei within reach at several wavelengths, thus adding important information on the nature of these extraordinary sources of infrared emission