This issue of MMR examines the 100 largest markets for grocery, drug and discount retailers, an annual exercise we have offered for several years.

This issue of MMR examines the 100 largest markets for grocery, drug and discount retailers, an annual exercise we have offered for several years.

Mostly, the rankings affirm the dominance of such market leaders as Walmart, Kroger, Publix, Costco, Walgreens and CVS. Without exception, these retailers dominate America’s largest markets to an extent even they could not have imagined a decade ago. The drug chain rankings, particularly, illustrate the dominance of Walgreens and CVS, though Rite Aid, recently returned from near extinction, is climbing impressively back to relevance in several markets.

The surprise here comes in the grocery category. Predictably, the leaders lead, as they have led for several years. But among the second-tier retailers, several not even represented in this country a decade ago have emerged as viable companies, retailers that turn up in market after market with business shares that place them in competition with grocery chains long used to dominance in individual markets.

Among these up-and-comers, two spring quickly to mind: Aldi and Trader Joe’s. Neither has U.S. roots; rather, both originated in Europe. Both have sprung from the same German retailing family. Both emphasize value, a concept that many U.S. retailers have relegated to a minor role, favoring price and selection as primary shopping inducements.

Neither of these emerging retailing powerhouses operates large stores; both prefer intimate settings — small, easy-to-shop outlets that offer reduced assortments of basic grocery merchandise. Both rely heavily on house brands to point up their value proposition. Indeed, their house labels form an integral part of their limited-assortment appeal. Private label, for these retailers, constitutes not an alternative to brand names but a viable ­shopping option that combines quality and price to offer a compelling value.

Both Trader Joe’s and Aldi have evolved as they have emerged in America. Each has expanded their basic assortments as they have grown the size of the stores they operate. Today, their merchandise mix includes categories and products they would have carefully avoided as recently as five years ago.

As for locations, these two retailers have successfully sought to expand their position in existing markets while opening new ones. And they have allowed their stores to serve as marketing ­vehicles.

As a result, most consumers who have come into contact with Trader Joe’s or Aldi know immediately that value is the name of their game. For variety, service, promotional advantages and marketing inducements, consumers would have to shop the larger, better-known grocery retailers that still dominate these markets. For a shopping experience largely reminiscent of another era, Trader Joe’s and Aldi are the logical choice.

So it is that these two recently arrived grocery retailers have had a significant impact on the U.S. grocery market. Rare is the city in which Aldi does not account for 3%, 4% or even 5% of sales. Rare as well is the municipality unaffected by Trader Joe’s. Combined, these two retailers are taking customers and sales from older, more established grocery retailers, at a time when these older companies, facing unprecedented market pressures, can ill afford to lose either.

One wonders, amid this creative activity, how much longer these newcomers will be ignored by a grocery industry that continues to believe that those retailing practices that worked so effectively for so long will work as well going forward.