This sixth edition of what was previously known as the Brief Teaching Edition of Volume A provides an introduction to the basic crystallographic data for space groups found in Volume A, for symmetry relations between space groups in Volume A1 and for subperiodic groups in Volume E of International Tables for Crystallography, to magnetic space groups and to the symmetry database that forms part of International Tables Online at https://it.iucr.org. It is designed for graduate students and young researchers who are new to the field of crystallographic symmetry, and includes many illustrative examples to help readers to understand and use these different kinds of information. Selected tables of symmetry data from the full volumes in the series are also included, making this a handy aid for classroom teaching. References are also provided to further specialized sources for those who need to go deeper into the subject and to textbooks for those who need more background information.