Wherever possible, Scholes tried to use primary source material, rather than summarizing other people's work. His preface to the First Edition describes how he played and read through thousands of sheets music, as well as reading thousands of concert programs and studying "old literature and long-bygone musical journals". From this research, he produced about fifty-five volumes of notes. Each of these was devoted to a separate branch of musical knowledge. He then sought peer review of each of these volumes with specialists in the particular branch of musical knowledge. Finally, these volumes were broken up and re-constituted in alphabetical order.

Scholes' intention was to produce a work relevant to a wide range of readers, from the professional musician to the concert-goer, "gramaphonist", or radio-listener. His work was aimed at a reader for whom it "will neither be beyond the scope of his pocket nor embarrass him by a manner of expression so technical as to add new puzzles to the puzzle which sent him to the book". The result was a work which was highly accessible to the general reader, as well as being useful for the specialist.

While scholarly and well-researched, Scholes' style was also sometimes quirky and opinionated. For instance, his original articles on some of the twentieth-century composers were highly dismissive, as were his articles on genres such as jazz. His entry on the can-can concluded "Its exact nature is unknown to anyone connected with this Companion."

He produced several revisions prior to his death (in 1958), with the last full revision being the 9th edition in 1955. The Tenth Edition, published in 1970, was a revision of Scholes' work by John Owen Ward. Ward considered it "inappropriate to change radically the characteristic rich anecdotal quality of Dr. Scholes' style." Although he brought some of the articles up to date, he left much of Scholes' distinctive work intact.

A distinctive feature of this Companion is a series of "imaginative" portraits of composers created by the artist Oswald Barrett (known as "Batt"). These consist of engravings (Bach, Beethoven, Brahms, Byrd, Chopin, Elgar, Handel, Haydn, Liszt, Mozart, Schubert, Schumann, Tchaikovsky, and Wagner),[1] and a frontispiece which is a colour reproduction of an oil painting of "Beethoven in Middle Life", described by Scholes as "the artist's personal gift to the volume" (see the Preface to the First Edition).