In the past few years, a crop of companies has been gaining steam with new approaches to primary care.

Rather than getting paid for each visit or procedure that a patient needs, startups are looking to change the way primary care is practiced, in many cases working to get paid a large fixed sum each month to take care of all of a patient's health needs.

In many cases, that means seeing fewer patients a year — hundreds, rather than thousands — offering additional services, or making the process of getting an appointment more convenient.

Read more: A new kind of doctor's office charges a monthly fee and doesn't take insurance — and it could be the future of medicine

And others are taking note. For instance, health systems including Utah-based Intermountain Healthcare and Pennsylvania-based Geisinger are taking similar approaches with some of their primary-care doctors. The federal government is planning to pay for care for some Medicare patients in a similar way too.

Investors have taken an interest in the model, pouring hundreds of millions in funding into some of the companies. And the space stands to bring in even more cash, from the public markets as well as private. One Medical in January kicked off trading on the public markets, surging to a $2.7 billion market cap in its first day of trading. Iora Health in February raised an additional $126 million.

The rise of some of these models — in particular venture-backed Iora, family-owned ChenMed, and private-equity-backed Oak Street Health — comes at a time when the market for Medicare Advantage plans has grown increasingly competitive.

As of last year, more than 20 million Americans were enrolled in private Medicare Advantage plans. People can typically choose to enroll in Traditional Medicare or Medicare Advantage plans when they turn 65. Either way, their health needs are largely funded by the US government.

Read on to see how the startups are shaking up the traditional way we do primary care.

This article was published on August 20 and has been updated.