Online grocery has quickly become a critical battleground for rivals Walmart and Amazon, and their ventures have created a ripple effect in the market for grocers and e-commerce players alike. 

Today, Amazon commands about 18% of the share of online grocery, according to a study from One Click Retail, while Walmart grabs about half as much. But, Walmart has a few powerful competitive advantages that Amazon and other e-commerce players don't.

For one, it's the largest grocer in the country. And secondly, there's a Walmart store within 10 miles of 90% of the U.S. population. That's been a critical part of making online grocery work at Walmart if you ask Tom Ward, Walmart senior vice president of digital operations, online grocery & last mile.

This time on the podcast, we spoke with Ward about how Walmart is positioning itself to win in online grocery, and specifically how stores come into play. Walmart is doing a lot of experimenting in the space right now with everything from driverless car delivery to in-store robots. Not all projects work perfectly from the start, but the company is learning a lot about what grocery delivery will look like in the future.

Also on the show, Grocery Dive Editor Jeff Wells breaks down how Walmart's new initiatives fit into the larger online grocery market. You'll hear all this and more in this episode, so sit back, relax and listen. You can stream the episode below or subscribe on iTunes or Stitcher.