This book is devoted to intralingual code-switching between Standard (SC) and Common Czech (CC), and addresses the following issues: linguistic variation; characterization of SC and CC; historical background and cause of the present opposition of the two codes; research findings on code-switching between SC and CC; requirements for sociolinguistics. The last topic points out the need for a third attitude towards national language stratification, i.e. support of code-switching in certain circumstances.