The Concertino for Clarinet and String Orchestra was completed in February 1958 and subsequent to its first performances in New Zealand, early overseas broadcasts were given by John McCaw, principal clarinet in the London Philharmonic Orchestra, with the BBC Northern Orchestra conducted by Norman del Mar.

The Concertino is a superbly crafted achievement, its texture enriched by the idealism of the post-war English pastoralists, the neoclassicism of Walter Piston (with whom Ritchie studied at Harvard in 1956–57), the delighted play of an imaginative harmonist, and the individualism of a New Zealander unconcerned with musical regionalism. Its witty and pointed rhetoric combines with the earthiness of a lover of nature to create a mainly joyous terrain which nevertheless trails within it cross-currents of doubt and loss. Regarded as a New Zealand classic, the Concertino takes its special force from what might be called the typically semi-detached New Zealand viewpoint.

Edmund Rubbra in Music and Letters, April 1964, described the Concertino as "a jaunty extrovert piece" and claimed "its virtues are in the effectiveness of the writing for both soloist and accompanying instruments". The response of a West Coast schoolboy to the first performance in Christchurch was equally enthusiastic: "You like it?" he was asked – his response: "You bet!".

The score, originally published in 1963 by Novello, is dedicated to Alex Lindsay and Frank Gurr.