SUMMARY: A population study of the box turtle (Terrapene c. carolina Linnaeus) was made during the years 1944 to 1947 at the Patuxent Research Refuge, Maryland. A thirty acre area in well drained bottomland forest on the flood plain of the Patuxent River was selected for intensive study. Similarly forested land extended in all directions from the study plot. Markers were established at eighty-three foot intervals over the study plot for reference in recording locality data. Individuals were marked by filing notches in the marginal scutes according to a code system. There were 2109 collections of study area turtles. Records of collecting sites and turtle behavior showed that in the bottomlands habitat cover is utilized extensively during the day as well as at night. Turtles not actively moving about are almost always found in or around brush piles, heaps of debris, and tangles of vines and briars. Gully banks and woods openings are used for sunning. Turtles are occasionally found in the mud or water of the gullies. The commonest type of night retreat is a cavity constructed by the turtle in leaves, debris, or earth. These cavities, termed 'forms,' may be used only once, but are sometimes used repeatedly, often at intervals of several days or more. Different turtles sometimes use the same form on successive nights. Weather conditions most favorable to turtle activity are high humidity, warm sunny days, and frequent rains. The most unfavorable influences are low temperatures and drought. On most summer days there are some active turtles but individual turtles are not active every day. Periods of activity are alternated with periods of quiet even in favorable weather. This behavior is most pronounced in early spring and late fall when inactive days are often more numerous than active ones. Adult turtles occupy specific home ranges which they maintain from year to year. The turtles living in the study plot retained their ranges even through a flood that completely covered the area. Maximum home range diameters were determined by measurements of the mapped ranges of individual turtles. The average range of adult males was 330 feet, adult females 370 feet. The difference between male and female ranges was not statistically significant. There was no evidence of defense of territory. Ranges of turtles of all ages and both sexes overlapped grossly. Turtles were frequently found near each other and no antagonistic behavior was observed. A trail-laying device was developed in order to follow individual travel routes. The trailer consists of a light weight housing fastened to the turtle's back. It contains a spool of white thread that unwinds as the turtle moves, thus marking its exact route. Turtles selected for this more detailed study were followed with trailers for a total of 456 turtle days. Maps illustrating their travels are shown. Normal movements within the home range are characterized by, (1) turns, doublings, detours, and criss-crossing paths completely covering the area, (2) interspersion of fairly direct traverses of the home range, (3) frequently repeated travels over certain paths or routes. Trailer records and mapped collection records both show that the maximum limits of the home range are ordinarily reached within a few days or weeks. This general procedure is varied by some turtles to include intensive coverage of only one portion of the range at a time. Some turtles have two home ranges and travel between them at infrequent intervals. One turtle showing this behavior was followed with a trailer for 161 days during 1946 and 1947. Trips outside the home range are made by some turtles. These include egg laying trips by females as well as trips of unexplained nature made by both males and females. Turtles from other areas occasionally occur as transients in the study plot. The size of the population was estimated on the basis of collections during on