For the second consecutive year, the growth of the overall prison population was half that of the preceding year and sharply lower than the record increases of 1975 and 1976. Or the states as a whole, the number of prisoners increased by 3 percent in 1978, compared with 5 percent in 1977, while the federal system experienced a 7-percent decline. The slowdown in inmate population growth after the mid-1970's is attributable to a variety of factors, notably the early release of prisoners from overcrowded facilities and diversion of less serious offenders into programs not involving incarceration. The aging of that segment of the population making up the post-world war ii baby-boom generation also made an impact. In the coming decade, these constraints on growth could be offset to a greater of lesser extent by prison construction programs underway in many jurisdictions and by the potential inherent in determinate sentencing laws for lengthening the average time served. The diversity of factors at work both within and outside the criminal justice arena precludes, however, an accurate prediction of future trends in the size of the nation's prison population. This report, one in the series published under the national prisoner statistics program, was prepared for the bureau of justice statistics by the U.S. bureau of the census. Figures and tables illustrate the text. The appendixes contain data tables, a description of the data collection method and a copy of the questionnaire, a technical note on custody versus jurisdiction, and explanatory notes.