Glassdoor just released its annual list of the best companies to work for, and as my colleague Peter Economy reported, it contained some surprises. But while it's fun to watch the rise and fall of specific firms on these lists, perhaps the more valuable question they raise is: What doesn't change? 

What is it that all the firms that top these lists (of which has its own) share, despite their different industries, cultures, and sizes? Figure that out and you'd have a roadmap to moving your own firm higher up the table, or simply making your little company more attractive to top talent. 

Handily, author Michael O'Malley has just done just that, visiting some 21 diverse companies who regularly appear at the top of these lists for a detailed investigation of their similarities. He recently wrote up his findings in a long, detailed HBR blog post. It's well worth a read in full if you're chasing "best places to work" status, but for the time crunched here are the five essential characteristics he uncovered: 

1. These companies take good care of their people. 

It's no surprise that the 'best companies to work for' O'Malley visited all offered excellent benefits like health insurance and 401k matching, often even to part-time employees. But he insists the generous perks are just one manifestation of a deeper ethos that all these companies share. "To them, a healthy culture is as important as a healthy balance sheet," he claims. 

O'Malley offers BAF as an example. When an employee suffered a terrible accident, "the company moved them from a third-floor apartment to a first-floor one in the same building, placing possessions just as they had been before and providing technology to stay connected during the recuperation process. (The employee had only been working there for a short period of time)," he writes. 

This might seem extreme, but O'Malley says all the great-to-work-for companies he visited shared this deep commitment to helping their employees not just work well, but live well. 

2. They help workers pursue their passions. 

The best places to work don't try to fit employees to jobs. Instead, they fit jobs to employees, finding ways to allow their people to pursue the types of work that they are most passionate about. 

For one pharmaceutical company that means allowing researchers on the payroll to "follow the science" rather than chase chase the highest profit. For other firms it meant sabbaticals, intensive training, or internal startup incubators to nurture employees' business or charitable ideas. 

"In short, the companies we visited had few life-draining dead ends analogous to those barricades at the end of long dark alleyways in horror films," O'Malley memorably sums up. "Rather, through developmental funding and frequent job moves, these organizations encourage people to self-examine their interests and to find what they truly excel at." 

3. They create real human connection. 

A ton of research shows having friends at work is a big predictor of job satisfaction, so perhaps it's no surprise that the best places to work create opportunities for employee bonding. 

That doesn't just mean lots of the usual team happy hours, softball games, and team-building outings. "The companies we visited celebrate special occasions together and recognize important life-cycle transitions," O'Malley reports. "BambooHR treats birthdays as paid holidays. Insomniac Games provides new parents with a custom onesie, art books, and toys, as well as a baby briefcase to help them keep their newborn's details organized." 

All this socializing might seem like a waste of time to some, but the most attractive companies understand that when it comes time to get down to work, teams are much more effective if they truly know, trust, and care about each other. 

4. They don't babysit their people. 

No one likes to have someone watching over their shoulder, but the very best employers don't just skip the micromanaging, they actively encourage employees to think like owners and take control of their work. 

Tom Caporaso, the CEO of Clarus Commerce, for instance, likes to think of himself as akin to a sports coach. "Once play begins, or people have proven they are capable of tackling projects on their own, there are a limited number of times that a manager will step in,"  O'Malley writes. "The field of play at Clarus is set by goals and budgets. Within these boundaries, it is up to the workers to execute." 

5. They allow employees to be themselves. 

"Fitting in is overrated," Melinda Gates recently insisted. The best places to work agree with her. While all of us have to make space for the expectations and preferences of others, at these companies employees nonetheless feel they can be their authentic selves at work. 

The Motley Fool, for instance, has a one sentence dress code: "Don't wear anything that would embarrass your parents." N2 publishing let the head of their mailroom, who happens to be a talented rapper, compose their theme song. 

"The ability to be authentic at your job is life-affirming: an outward expression of who we are and what we stand for. In this regard, authenticity also has a nonobvious effect. People who behave in accord with their values have stickier work ethics. They are more morally engaged, less deferent to circumstance, and will choose principle over the enticement," O'Malley writes. 

How many of these characteristics does your company share?