Mitie Group PLC (pronounced "mighty") is a British strategic outsourcing and energy services company. It provides infrastructure consultancy, facilities management, property management, energy and healthcare services. It has a head office at The Shard in London and more than 200 smaller offices throughout the United Kingdom and Ireland. It is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index.

Mitie was founded by David Telling and Ian Stewart as MESL in 1987. One year later, the company was listed on the London Stock Exchange for the first time. It merged with Highgate & Job in 1989, after which it was renamed the Mitie Group.

Throughout the 2000s, the company pursued a strategy of growth through the acquisitions of various other businesses. In March 2006, it acquired Initial Security, a leading security business. During 2007, Mitie acquired Robert Prettie & Co. Ltd in exchange for £32.7m and incorporated the specialist plumbing, heating and mechanical services business into their Property Services division. In 2008, Mitie continued its strategy through the acquisition of Catering Partnership and DW Tilley; the latter purchase allowed Mitie to expand its roofing services nationwide. During 2009, Mitie completed the acquisition of Dalkia Facilities Management in exchange for £130m, which bolstered its Technical Facilities Management capability; it also expanded into social housing through the purchase of Environmental Property Services (EPS) for £38.5m. During 2010, Mitie acquired the integrated facilities management business of Dalkia in Ireland.

Mitie made its first acquisition in the health and social care sector in October 2012, when it spent £111 million on the homecare firm Enara. In April 2013, Mitie's chief executive, Ruby McGregor-Smith, was made non-executive director to the board of the Department for Culture, Media and Sport. During February 2014, Mitie introduced its new visual identity.

Between 2013 and 2015, cleaning staff employed by Mitie at various high-profile locations, including the Royal Opera House, the Houses of Parliament, the law firm Clifford Chance, First Great Western train services, and various NHS hospitals, held demonstrations against low pay.

In February 2014, Mitie announced an eight-year contract with the Home Office, making it the largest provider of immigration removal centres in the United Kingdom. Almost two years later, Mitie came under fire for its management of the immigration centres after the prison inspectorate stated that the facilities were "dirty", "rundown" and "insanitary". Mitie has continued to be involved in the sector.

The firm secured a cleaning contract with Royal Cornwall Hospitals NHS Trust during June 2014 valued at £90m over seven years. Sick pay cost £1.2m in its first eight months, compared with £280,000 for the NHS in the previous financial year; UNISON blamed the rise on staff stress, which it claimed had been caused by mistakes on pay. Such difficulties were not typical to Mitie's other NHS cleaning contracts, although there has been some criticism over their higher cost than other providers.

In November 2014, Mitie acknowledged that its homecare business was less profitable than had been anticipated and that it was struggling to recruit and retain sufficient numbers of care workers. During July 2015, East Sussex County Council reportedly ended a £2 million contract with Mitie to provide home care over allegedly poor standards of care provided.