We have made temperature‐dependent photoluminescence and absorption measurements of the dominant excitonic transitions in high‐quality lattice‐matched and strained single and multiple quantum well systems grown by molecular‐beam epitaxy. GaAs/AlGaAs, InGaAs/InAlAs, and InGaAs/GaAs single quantum wells grown under the optimal conditions exhibit liquid helium photoluminescence linewidths (HWHM) equal to 0.39, 3.2, and 2.7 meV, respectively. GaAs/AlGaAs multiple quantum wells of well size 60, 96, and 200 Å exhibit low‐temperature linewidth (HWHM) of 1.3, 1.6, and 2.2 meV, respectively. Strained InGaAs/AlGaAs multiple quantum wells (120 Å) have 3.5 meV HWHM linewidth. These excitonic linewidths are among the smallest reported for each system. The excitonic peaks are clearly present in all material systems up to 300 K. The finite exciton linewidth at the lowest temperature is attributed to inhomogeneous broadening due to interface roughness and well size fluctuations, while the temperature broadening results from homogeneous interactions of excitons with both acoustic and optical phonons. Based on this assumption we have calculated the homogeneous part of the linewidth and consequently the exciton lifetime at higher temperatures by careful fitting of experimental data with Gaussian and Lorentzian line shapes. The results are interpreted in terms of exciton–phonon interactions.