With some tech jobs, employers are fine if a candidate can simply demonstrate that they have the necessary skills. With others, though, certifications are heavily recommended—if not outright required. But which tech professions feature the most employers requesting certifications? Read on.

For this analysis, we relied on Burning Glass, which collects and analyzes millions of job postings from across the country. That allowed us to break down, for each profession, the percentage of job postings that asked for certifications. Here’s the list:

As you can see, if you’re interested in becoming a network/systems administrator, a very healthy portion of employers will want you to possess certifications. And that certainly makes sense—many employers are cautious when it comes to hiring people to set up and manage their IT infrastructure, and they want to make sure that their new employee can actually do the job.

But which certifications do employers actually want in conjunction with network/systems administrator jobs? Fortunately, Burning Glass gives us a breakdown of that, as well:

With other jobs on this list, though, certifications aren’t quite as important to many employers. For example, only 1.1 percent of the million-plus job postings for software developers and engineers requested certifications; this is unsurprising, as many companies simply want developers and engineers who know the necessary languages and tools, and have a track record of building fine products.

In fact, many employers aren’t demanding super-advanced degrees, either; for these tech roles, a bachelor’s degree tends to be the average. Check out this other list compiled from Burning Glass data: 

Specialization and certifications might not be necessary for many jobs, but those things can help you advance your career (and sometimes land a significant pay boost). For example, a network/systems administrator with cybersecurity certifications can find many more opportunities opening up. In a similar vein, software engineers or project managers with artificial intelligence (A.I.) and machine-learning experience can radically increase their salaries and other kinds of compensation.