The principal uses of statistics in library planning may be illustrated by examples from the state of Illinois. State law specifies that the Illinois State Library compile and publish statistics on libraries. State agencies also play an important and expanding role in this effort. The state library now compiles statistics on all types of libraries, and attention is being given to analysis of this data. Local librarians can aid the statewide data collection program by maintaining accurate records. These records, when interpreted to the community, also have a public relations value for the local library. The uses of library statistics can be divided into several general categories: statewide and institutional comparison and evaluation, legislative justification, administration of library standards, manpower planning, and budgeting. Those engaged in library planning need not be reminded of the importance of accuracy and comparability in statistical data. The cost of data collection can be reduced through the use of scientific sampling. Inservice training should be implemented to change the negative attitudes of librarians toward measurement, since this is a major barrier to improved statistical reporting. (Author/SL)