Thea Musgrave, doyenne of Scottish composers, is 80; and in Glasgow, Edinburgh, Aberdeen, Inverness, Perth, Dundee and Stirling, as well as in England and the US, she is being feted with performances of new works and older ones (Rainbow, composed in 1990 for the opening of Glasgow Royal Concert Hall, was played during the summer by the RSNO at the London Proms). Though she has lived in the US for nearly 40 years, her name girdles the globe and her inspiration remains undiminished. For the dashing strings of the Scottish Ensemble, she has been commissioned to write something apt and has responded with the topically entitled Green, which receives the first of a chain of performances in December, starting in Aberdeen.

Born in Barnton - Edinburgh's greenest suburb - Musgrave studied with Hans Gal at Edinburgh University before spending four years as pupil of the great Nadia Boulanger in Paris. Like her slightly older contemporary, Iain Hamilton, she severed her Scottish links at a time when her homeland seemed musically barren and did nothing to hang on to her. Six years of lecturing at London University led to a Californian professorship and then to life in Norfolk, Virginia, with husband Peter Mark, viola virtuoso and conductor of the Virginia Opera.

But if Scotland seemed a thing of the past, the rise of Scottish Opera in the 1960s and the internationalising of the Scottish National Orchestra under Sir Alexander Gibson proved otherwise. Suddenly she found herself in demand back home. Her masterpiece, Mary Queen of Scots, was unveiled at the 1977 Edinburgh Festival. Her Horn Concerto, with Barry Tuckwell as soloist and Gibson as conductor, was the highlight of the SNO's second visit to Vienna's Musikverein.

Today she is in the happy position of being a Scot who lives elsewhere but is appreciated everywhere. Green is a work about conflict, represented, she says, by the clash of opposing musical forces, one of them melodic, tonal and led by the first violin; the other discordant, suffocating and inexorable, with the double-bass as protagonist. As the threat of the latter increases, reaction to it grows stronger. But after appeals from a solo violin, viola and cello, the original melodiousness is fragmented and dies away. Many parallels to this, she asserts, can be drawn from life. The title refers to youth, and to the plant life on which everybody depends.

Such conflicts dominate much of Musgrave's music, from the Concerto for Orchestra of 1967 - where the clarinet section challenges the conductor's authority - onwards. In her Clarinet Concerto, written for Gervase de Peyer, the soloist moves around the platform, forming disruptive splinter groups with other players. In her Horn Concerto, the soloist summons Wagnerian horn-calls from colleagues placed around the audience. In her Viola Concerto, written for her husband, the viola section at one point rises in the soloist's support - and comes close to obliterating him. Though these are abstract works, the players have powerful, individual, almost operatic identities. The works are music dramas of a subversive sort.

One of the latest of them, entitled Points of View, has horn, trumpet, oboe, cor anglais and violins as competing voices. Premiered by the Manchester Camerata in February, it will be performed by Nicholas Kraemer (a revered exponent of Musgrave, who is herself an accomplished conductor) and the Scottish Chamber Orchestra in Glasgow and Edinburgh on December 12 and 13. But the early chamber concertos are similarly disputatious, particularly the humorous No 2, a tribute to Charles Ives (one of Musgrave's heroes), filled with clashes between popular tunes and their accompaniments. A performance of this, too, would be welcome, as would a dramatic new Scottish Opera production of Mary Queen of Scots.

Meanwhile, there is humour of the lightest sort in Taking Turns, as the Scottish Flute Trio will disclose at Duff House, Banff, on November 13, with repeat performances at Bieldside, Aberdeenshire; the Tolbooth, Stirling; Glasgow University; and the Huddersfield Contemporary Music Festival.

In this work, explains the composer, all three flautists in turn will play each of the three instruments - piccolo, flute, alto flute - required for a musical dialogue ranging from the lowest note of the three alto flutes through a mischievous interlude for the piccolos to a finale in three clashing keys.

On November 6, the BBC Scottish Symphony Orchestra, making its first appearance with the gifted young Rory Macdonald as conductor, will perform Aurora, Musgrave's orchestral dawnscape, composed for student players in Los Angeles and already presented by the BBC SSO during its Chinese tour eight years ago. And then on December 8 and 9 comes a two-day Musgrave marathon at the Sage in Gateshead, where the Northern Sinfonia will be surveying 14 of her works, among them The Seasons, an instrumental poem as vivid as Vivaldi's, and Lamenting with Ariadne, where the abandoned Ariadne auf Naxos is portrayed by a solo viola and her rescuer by a trumpet. Interwoven with six other instruments, this is Strauss's opera - complete with joyous ending - pared to its essence.

The Gateshead event, suitably entitled All Eyes on Thea Musgrave, deserves to draw her Scottish admirers south of the border. It will include, as an extra incitement, the premiere of Take Two Oboes, a jeu d'esprit composed specially for the occasion. Continuing Musgrave's association with the brilliant Nicholas Daniel, it forms a follow-up to the Oboe Concerto he played with the Scottish Chamber Orchestra in Orkney in 1995, when the sun god Helios (personified by Daniel) activated his wind-playing troops around the perimeter of the orchestra, resulting - as The Herald put it at the time - in a classical music jam session, as exhilarating as anything Musgrave had written until then. It, too, will feature in the Gateshead survey.