The way in which animals use the physical and biological resources in habitats is an important aspect of their behavioral ecology. Here, we studied the activity and habitat use of the European glass lizard in two habitats in southeastern Bulgaria during the spring and summer of 2015. We registered behaviors such as basking and movement, and we recorded hiding locations. We also attempted to capture the individual mark of every observed individual, to determine its sex, age, and body temperature, immediately at capture. In parallel, essential environmental parameters were identified: temperature of the air near the lizard, substrate temperature, dominant plant species, and humidity. The results showed that there were seasonal differences in the activity of the lizards and the variables of the environment. In Habitat 1 where most of the glass lizards were registered we observed habitat segregation. The habitat selection of adult glass lizards was closely connected to the presence of shrubs but not of forest. We discuss these findings in relation with proximate and ultimate factors, determining the habitat use of European glass lizards. Extended knowledge of habitat use of P. apodus is highly relevant to its future preservation.