The core of the work consists of chapters on seven languages: Gothic, Old Norse, Old Saxon, Old English, Old Frisian, Old Low Franconian, and Old High German. Each offers a brief history of the language's speakers and a survey of texts. Then come some sample passages, with marginal glosses of English and German cognates and a full glossary following (and word-for-word translations in an appendix). A look at the language's phonology and morphology considers features that are important in comparison to other Germanic languages, distinctive, or just interesting.
Each of these chapters also covers one specialised topic: "The Assignment of Sounds to Letters" in Gothic; Old Norse runes; Germanic alliterative verse; aspects of Germanic syntax; the problems of comparing languages of different ages, with "Old" Frisian half a millennium younger than Old English and nearly a millennium younger than Gothic; manuscript interpretation in "The Philological Assessment of the Wachtendonck Code"; and the High German Consonant Shift and the range of Old High German dialects. A selection of further reading suggestions accompanies each chapter, making it a good springboard for more specialised study.
A final chapter looks at the limitations of the traditional Germanic family tree and surveys different theories for the history of the Germanic languages. These have to encompass "a fluid, changeable situation in which dialect communities may alternately diverge, diverge only in part, converge, converge only in part, and otherwise behave like human groupings rather than biological species trees".
Old English and its Closest Relatives starts off assuming no background in linguistics or knowledge of foreign languages: the first chapter explains the different relationships of German and French to English and introduces concepts such as "cognate", declension and agreement. The bulk of the book is technical enough, however, that readers with no experience of a second language (or phonological and morphological linguistics) will find it intractable.
The obvious audience for Old English and its Closest Relatives is students of Old English — hence, presumably, the title — or Old Norse. But anyone who has some experience studying dead languages (or German or Dutch) and is curious about the history of the Germanic languages should find it fascinating.