A description is given of the experimental system which was used for obtaining Ramsey fringes with an atomic beam for the Ca 657 nm line, and for the system which is being set up to obtain fringes with a large absorp tion cell for various molecules in the 10 vim region. Details of the cat's eye and segmented retroreflector optical systems are discussed. Results obtained with Ca include fringe widths as small as 1 kHz HWHM , resolution of the recoil splitting, and resolution of second-order Doppler broadening and shift. The experiment at 10 \sxs\ is in progress and has already yielded a 1.25 kHz linewidth (HWHM) for the single zone signal with the SF, molecule. Introduction. - The optical Ramsey fringe technique has been developed over the last few years to the point where extremely high resolution can now be obtained. Fringes have been observed for several atoms and molecules, including Ne (by Bergquist, Lee and Hall > ), CH, (by Bergquist, by Kramer, and by Baba and Shimoda ), Ca (by Barger, Bergquist, English and Glaze ' ' , and by Helmcke et al., ), and SF, (by Borde et al., ). The use of this technique in investigations of the Ca 657 nm line at the National Bureau of Standards has produced linewidths as narrow as 1 kHz HWHM. This resolution has resulted in 1) complete resolution of the 23 kHz recoil splitting, 2) observation of the power contraction of this splitting, and 3) reso lution of the second-order Doppler broadening and shift (1.7 kHz) and the attendant resolution-dependent distortion and shift of the Ramsey fringe profile. Experiments using the Ramsey technique in the 10 iJm region with OsO. are now under way at the Laboratoire de Physique des Lasers. The experimental parameters should yield line- widths of less than 100 Hz and result in resolution of the superfine and hyperfine structures present in the 10 Via region spectra of many molecules. In this paper we shall discuss some of the experimental techniques which have been used in the visible and 10 \m experiments.