The Big Four accounting firms, or professional services networks as they're sometimes also known, are multinational conglomerates that have grown to become some of the largest organisations in the world.
They're traditionally known for their audit work - an inspection of a company's accounts that is legally required once a year - which continues to be their main source of revenue. It's reported that, between them, the Big Four audit 99 per cent of FTSE 100 companies.
They also provide other services including tax work, consulting services and corporate finance advice.
Why work for them?
Typically, the Big Four employ the most graduates in this sector and offer many of their graduate employees sponsorship and practical support through an accountancy qualification or another business-related course of study.
Roles here are well paid - the average starting salary at the Big Four firms is £29,000 - but not quite as lucrative as those in law or investment banking.
As well as offering you great opportunities to progress with professional services, starting your career at a Big Four firm can be a great route into a career in banking or even a corporate board role.
Who makes up the Big Four?
The Big Four is made up of Deloitte, EY, KPMG and PwC.
UK headquarters: 2 New Street Square, London
Global revenues 2012/13: $32.4 billion (£19.9 billion)
Graduate hires in 2013: 1,200+
UK employees in 2013: 14,529
Best known for: Audit, Tax
The firm is often regarded as having an outgoing and ambitious culture and is known for hiring sharp, analytical graduates.
Deloitte has a history of winning impressive clients including consumer products company Procter & Gamble, which it's audited for over 100 years.
The firm's main rival is PwC and together they audit 136 of the FTSE 250, with Deloitte edging ahead with 69 clients. Unlike PwC, Deloitte's main source of revenue comes from its US operations - Europe is currently its second biggest source of revenue - and in 2012/13 its global revenue overtook that of its main competitor.
UK headquarters: 1 More London Place, London
Global revenues 2012/13: $25.8 billion (£15.8 billion)
Graduate hires in 2013: 700
UK employees in 2013: 11,000+
Best known for: Audit & Assurance, Consulting
EY is one of the smallest of the Big Four firms in the UK by number of employees, and is reputed to have a slightly more relaxed and friendly working atmosphere than the others. It's also consistently recognised for its work promoting LGBT rights in the workplace.
It's also one of the smallest firms in terms of revenue, and out of the Big Four it audits the least number of FTSE 100 companies.
However, in 2013 EY's UK business was the second most profitable of the Big Four. Its main rival is KPMG, and EY is making plans to join the firm in Canary Wharf.
UK headquarters: 15 Canada Square, London
Global revenues 2012/13: $23.4 billion (£14.4 billion)
Graduate hires in 2013: 800+
UK employees in 2013: 10,752
Best known for: Consulting, Tax
The name KPMG is made up of the initials of the firm's founding members and, although it has only existed in its current form since the late 1980s, the Dutch-born firm can trace its history back 300 years.
It's known for its smart graduates, collaborative atmosphere and allegedly rather eccentric culture.
KPMG is probably the most Europe-focused of all the Big Four. In 2012/13, its UK profits jumped by 27 per cent to £455 million. In comparison to the other Big Four firms, KPMG is known for its consultancy work.
UK headquarters: 7 More London Riverside, London
Global revenues 2012/13: $32.1 billion (£19.7 billion)
Graduate hires in 2013: 1,200+
UK employees in 2013: 17,420
Best known for: Assurance, Tax
PwC is viewed as the most prestigious of all the Big Four to work for and employees there are very conscious of that fact.
PwC is also known to invest a lot in training and development for its employees.
It may have recently lost its crown as the top firm in terms of global revenue, but in the UK, where most of its work is, it's still leader of the pack. Although audit and tax are big earners in the UK, the firm's consultancy service grew at the fastest rate in 2012/13.
While the Big Four may have a monopoly on FTSE 100 clients and some outstanding career opportunities for graduates, bigger isn't always better.
There are several accounting firms at the top of the mid-market that also have exceptional reputations and an international presence.
For example, Grant Thornton audits fast-growing AIM-listed clients and even one of the Big Four, so it and other firms like it can certainly provide interesting work. There are also firms that specialise in offering services to particular sectors, such as arts and media.
Finally, the smallest accounting firms could offer you a wider variety of work, greater recognition from senior colleagues, and a less demanding work schedule than the Big Four.