To help you make sense of the landscape of professional services firms that are recruiting graduates, we've split the most important firms up into three groups according to their size, and provided a brief description of each.

The Big Four

The world’s four largest professional services firms – DeloitteEYKPMG and PwC – are significantly bigger than their nearest competitors. With combined global revenues of $129 billion in 2014/15, the ‘Big Four’, as they’re known, currently audit all but one of the FTSE 100. 

You'll find all the information you need to get to grips with these financial behemoths in our article comparing the Big Four accounting firms.

Mid-tier accounting firms

With a monopoly on FTSE 100 clients, the Big Four firms are able to offer outstanding career opportunities for graduates, 

However, bigger isn't always better – there are a number of accounting firms at the top of the mid-market that also boast exceptional reputations and an international presence.

Grant Thornton, for example, audits fast-growing clients listed on the AIM (a sub-market of the London Stock Exchange) and even one of the Big Four. It (and other firms like it) can certainly provide graduates with interesting work. There are also firms that focus on particular sectors, such as technology and media.

Baker Tilly

Baker Tilly is known for being a good-value alternative to the Big Four. It's well known for its work with clients in the arts and media sectors, and also advises a large number of AIM-listed businesses.

The firm reported global revenues of $3.6 billion in 2014/15, or which $1.2 billion was earned from its operations in the Europe, Middle East and Africa (EMEA) region. 

BDO

Headquartered in Brussels, BDO is one of the closest challengers to the Big Four in terms of the size of its UK business, reporting a total income of £400 million in 2014/15. It's also the only non-Big Four firm to audit a FTSE 100 company. 

BDO has the largest international network of any mid-tier firm and saw revenue growth of 22 per cent and 10 per cent for the Americas and Asia Pacific regions during 2014/15, respectively.

Grant Thornton

Grant Thornton makes the most money in Britain out of the top 60 UK firms outside of the Big Four (it had a UK turnover of £521 million in 2014/15), though the firm takes in less than a third of nearest rivals Ernst & Young and KPMG.

Grant Thornton is a market leader in audit work, and is the official auditor to the Takeover Panel. It also makes significantly more of its profits from corporate recovery work than its non-Big Four rivals.

Mazars

Mazars, headquartered in France but with 18 UK offices, has a particularly strong presence in continental Europe and has the largest network in the region after the Big Four. The firm is also reported to pay its staff particularly well for a mid-tier firm.

PKF

PKF is particularly strong on consultancy, making over twice as much from this income stream as its nearest non-Big Four rival (though nowhere near as much as the likes of Deloitte and KPMG). PKF organises itself as a network of individual firms rather than one global entity.

RSM Tenon

RSM Tenon has the distinction of being one of the first professional services firms to list on AIM and remains one of a very few professional services firms in the UK top 60 to have done so. 

At last count, the company also had the highest number of UK offices out of any of the top 60 – with 50 regional outposts it even beats PwC's 40 offices.

Smaller firms

Smaller accounting firms are a viable alternative to the Big Four and mid-tier firms. They can be a great option if you’re looking for a wider variety of work, greater recognition from senior colleagues, and a less demanding work schedule.

At the larger end of this bracket of firms sit Crowe Clarke Whitehill, Haines Watts Group, Kingston Smith, Moore Stephens, Smith & Williamson and UHY Hacker Young.

You're likely to work with smaller clients across a broader range of industries. You may also get exposure to a number of different areas of professional services, say, audit and tax, which are kept separate at most larger firms.