Many people struggle with trying to find firms to apply to for spring weeks and summer internships, and in fairness, if you don't know much about the Finance industry, it can be very difficult to wrap your head around what exists and what each firm offers. It gets even more complicated when you realise a lot of firms will offer more than one service - for example; Barclays is a known Bulge Bracket Investment Bank, but it also offers wealth management, retail banking, asset management, and corporate banking services, among others (If you're unsure of the service lines I've just mentioned, have a look at our previous post to familiarise yourself).
Here are some helpful definitions for different IB firms that you may hear, and that you can use to differentiate between them.
Bulge Bracket (BB) Investment Banks
Bulge Bracket (or BB) banks are large, international investment banks who tend to oversee the largest deals and handle very large clients. The bulge bracket firms are the largest in terms of numbers of offices and employees, and they regularly handle multibillion-dollar M&A deals.
Notable BBs;
Goldman Sachs
Deutsche Bank
Credit Suisse
Morgan Stanley
Bank of America
JPMorgan
UBS
Barclays
Elite Boutique (EB)
Elite Boutique banks (or EB) more closely resemble bulge bracket banks in regard to the value of the deals they manage. However, they are generally more specialised in the markets they operate in. Elite boutiques tend to have sizeable nationwide and international presence, but not to the same scale as BB banks. They usually do not provide a complete range of investment banking services and may limit their operations to M&A and restructuring.
Notable EBs;
Lazard
Moelis & Co
Evercore
Qatalyst Partners
Middle Market (MM)
Middle Market banks (or MM) generally occupy the middle ground between smaller regional firms and the massive BB banks. Middle-market banks usually work on deals that begin around the regional level and go up to near the bulge bracket level, typically ranging from about $50 million up to around $500 million or more. Middle markets are usually also in the middle ground as far as geographic reach, having a substantially larger presence than regional boutiques but falling short of the multinational scope of bulge bracket banks.
Notable MMs;
KBW
Piper Sandler
Cowen Group
Houlihan Lokey
Regional Boutique (RB)
Regional Boutique banks (RB) are the smallest of the investment banks, both in terms of firm size and typical deal size. Regional boutiques usually have very few employees and a limited national presence. Because of the small size of most regional boutiques, they do not typically offer all the services offered by BB investment banks, and may simply specialise in a single area, such as handling M&As in a particular market sector.

Application Trackers
If you're going to believe one thing, it's that application trackers are your friend. You don't want to be sitting in a few months time forgetting where you applied, who you applied to, and at what stage you're at in each process. I remember spending multiple hours just formatting mine ahead of application season for summer internships because I missed out on spring weeks, but it was 100% worth it.
Many websites offer a form of application tracker, but these aren't always personalised to exactly what you're looking for, and many are from US sources, which have a different timeline to UK firms. If you have the time, creating your own application tracker is really worth it. In this way, you can track the firms you're actually interested in.
Luckily, for both you and me, we have been saved by our friends at LSESU who have provided a very useful spreadsheet that lists a large number of firms, detailing the application process, deadlines, and main service lines of each. Feel free to check it out using the link below:
How Many Firms Should I Apply To?
As many as possible. Whilst the difficulty of scoring a successful application varies whether or not you're applying for summer or spring experiences (with the former being the more difficult of the two), apply to as many firms as you can. Even if you're the crème de la crème of applicants, the world's best financial modeller, or the smartest in your cohort, you should expect to be rejected from a lot of your applications. Firms have high rejection rates, especially in more competitive areas like IB. Don't take this as a sign of failure; use their feedback to brush up on your weaknesses and hone your application skills. Many people will apply to 50+ firms only to receive one offer, especially for summer internships. Spring weeks are a lot easier, but don't expect to have all of your applications come back positive.
Don't put all your eggs in one basket, either. If you've run out of firms to apply to in your desired sub-industry, branch out to others that you may also be interested in. Research the different pipelines to your desired endpoint - are you looking to move into Private Equity? Then take a step back and see how you can get there; whether straight after having some experience in an Investment Bank, or after getting qualified as an accountant and moving into banking and PE that way.