The robots are coming. Fortunately, they’re bringing groceries and takeout with them. Welcome to the world of delivery robots: one of the fastest-growing and most competitive markets in robotics.

The idea behind these bots is simple: The customer orders an item, that item is loaded into or onto the robot, and then the robot travels to the customer to drop it off. But that’s not stopped multiple intrepid companies from exploring their own innovative approaches to the challenge.

Here are six of the biggest names to watch out for when it comes to delivery robots. Coming soon to a sidewalk near you — if they’re not there already.

With its Star Trek-sounding name, it’s no surprise that Starship went boldly where no other robotics company has gone before; helping invent the modern delivery robot in the process. The company was founded in June 2014 by Skype co-founders Janus Friis and Ahti Heinla.

It’s currently operating in several cities around the world, as well as numerous university campuses where it’s a favored late-night snack food delivery method. The sidewalk-navigating robots are already becoming a regular sight in many locations, and Starship is racing ahead to ensure it maintains its first-mover advantage.

Debuting January 2019 and delivering packages to Amazon customers in Snohomish County, Washington, Amazon’s fleet of autonomous Scout delivery robots have since expanded to the Irvine-area of California and, most recently, Franklin, Tennessee, and Atlanta. Customers in these areas do not have to sign up for any special Amazon Robot service. Instead, they simply place their order normally and, where possible, a robot will be dispatched to deliver it. Currently, the robots are accompanied by a human Amazon Scout Ambassador to ensure everything is working correctly.

Amazon Scout was based on Amazon’s 2017 acquisition of robotics company Dispatch. While Amazon is not the first company to get in on the delivery robot market, it has a great chance at dominating it. Delivering billions of packages a year, Amazon is well-equipped to capitalize on new delivery technologies in a way that few other companies are — or will ever be.

What would you get if you crossed the delivery robot business model with Boston Dynamics’ dog robots? Probably something like Aida, a robot from Unsupervised A.I., a company that’s delivery robots look a little different (and more canine-inspired) than the box-on-wheels model proffered by Starship and Amazon.

The size of large dogs, these Aida robots could be dropped at curbside before scurrying the last bit of their journey to deliver packages of up to 30 pounds. Unlike alternative delivery bot solutions, these robo-couriers could climb over obstacles and successfully maneuver challenging terrain such as steps.

However, the rollout of these robots is still far behind some of the other companies on this list — although dog robots made by other companies are now being used for tasks like oil rig inspection in the real world. Still, when it comes to a unique approach to delivery bots, Unsupervised A.I.’s creations most certainly deserve a spot (or, as Boston Dynamics might say, a Spot) on this list.

Bearing a name highly reminiscent of Forbidden Planet’s Robby the Robot, Robby Technologies‘ creation is a delivery robot boasting six-wheel design and an impressively versatile ability to climb curbs and hilly terrain to bring you your food. The company was founded by two Massachusetts Institute of Technology grads in computer vision and robotics, Dheera Venkatraman and Rui Li, and has been in operation since 2016. It hasn’t made quite as much of a splash as some of the other companies on this list but has already inked a deal with PepsiCo, so definitely don’t count it out as a contender.

When you go to the store, you can choose between taking a grocery bag (if you’re only buying a handful of items) or taking your car (if you’ve got a lot more to pick up). Most of the delivery robot options on this list are designed for a grocery bag-sized purchase. But what if you want to place a bigger order? That’s one of the unique selling points of Nuro, a robotics company that’s established partnerships with Kroger, CVS, Domino’s, and Walmart.

Nuro’s larger-sized delivery robots are more like self-driving cars than anything. They drive on the street, not the sidewalk, and they can carry multiple bags of groceries (or other items) where many delivery robots are limited to just one or two. One of the two brains behind it (alongside Jiajun Zhu) previously designed the algorithms used in NASA’s Mars rovers and helped develop Google’s self-driving car project.

Nuro launched its unmanned delivery service in December 2018. It has been testing in Texas and Arizona, and earlier this year got permission to expand to California, too.

Many of the robots on this list take different approaches to deliveries, but they all share one thing in common: They’re “outside robots.” But what if you need a robot to carry out deliveries indoors? This is where Savioke’s Relay robot comes in. No, the company is not expecting that most of us will shell out for indoor robot butlers that will fetch us sandwiches from the kitchen and then trundle through to the living room where we’re relaxing (although that doesn’t sound a terrible idea).

Instead, it’s aimed at sectors like hospitality, where its delivery bot can be used for room service and similar applications. Should a hotel guest wish for a toothbrush or towel, the front desk employee can place the items in Relay’s enclosed compartment, tell it where to go, and then allow it to head off to make the delivery.

The three-foot-tall robot uses Wi-Fi, along with on-board sensors and cameras, to navigate corridors and corners. (It’s even able to summon elevators.) When it arrives, the room guest gets a notification and picks up the item they need. Savioke’s Relay robots are already being used at multiple hotels.