The western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae) is a key pest of fruit, vegetable, and field crops in the western United States, but many aspects of L. hesperus ecology are poorly documented. A sound understanding of oviposition behavior and characterization of the phases of embryonic development would be useful in studies of interactions between L. hesperus and its hosts, and in efforts to better understand the developmental consequences of low temperatures. Because L. hesperus insert their eggs into the host, most of the egg is obscured from view, and some aspects of oviposition and subsequent egg development cannot be observed directly. A novel observational method which took advantage of the propensity for L. hesperus to oviposit in semi-transparent sheets of agarose was used to observe oviposition and subsequent embryonic development. Lygus hesperus females stylet-probed prospective oviposition sites and during oviposition the ovipositor followed the path of the final probe. Oviposition, from insertion to withdrawal of the ovipositor, required ∼30 seconds. Identifiable phases of embryo development included egg swelling, katatrepsis, appearance of body segments and appendages, development of red pigmentation in the eyes and terminal antennal segments, and formation of the 3^rd embryonic cuticle. These phases were observed at about 0.3, 0.4, 0.5, 0.6, and 0.8 of the total duration between oviposition and hatch, respectively. Infertile eggs did not exhibit any of these phases. Our descriptions of embryonic development will facilitate the study of L. hesperus egg biology and ecology, and permit estimates of egg population age structure and prediction of egg hatch.