Millions of people stream into Ikea stores every year to fill their carts with inexpensive yet attractive enough bedside lamps, jauntily named bookshelves, and clever storage solutions. All this stuff must go from store to home somehow, and until recently, it was transported in large plastic bags. Last year, Ikea started charging a nickel for every plastic bag, saving more than 35 million of them from being dumped in landfills. This October, the store will phase out disposable bags altogether, and the only way to lug home a decade’s supply of tea lights will be in a reusable 59-cent jumbo tote or your own handy carrier.

Thanks in part to its sensible Swedish roots and the European maxim that smarter is smaller, Ikea has gone greener in the past few years with tree-planting projects, flat-pack shipping, living roofs, and solar panels. Other big boxes are starting to catch up: The mass furniture chain is no longer alone in its quest for sustainable solutions.

Wal-Mart made a big splash with its recent announcement to go green, rolling out a list of impressive initiatives, creating a viable prototype store that is 25 to 30 percent more efficient than current stores, and installing concrete floors made from recycled content. Competitor store Target is part of the U.S. Green Building Council’s new Portfolio Program pilot, in which 40 companies have committed to integrating green building design, construction, and operations into their standard business practices using LEED technical standards and guidance. Target stores will soon include heating and cooling systems that reduce energy needs by 20 percent, as well as such mundane but important elements as low-flow bathroom fixtures and fewer bulbs in their lights. Noting the store’s 15-year-old solid-waste recycling program, which supplies an $80 million revenue stream, Target’s manager of strategic development initiatives, David Luick, says such green programs “make good business sense and good sense for the environment.”

However, it’s not all coming up roses for big boxes. “Sustainability means conducting business in a way that enhances health, well-being, and inheritance in terms of the environment for future generations,” Michael Marx, executive director of Corporate Ethics International, explains. “Every acre of Wal-Mart is equal to at least 100,000 acres in terms of resource demands on the planet. Its footprint is huge.”

Others, like Joseph Feller, agree. Feller is part of a group called Vallejoans for Responsible Growth that is battling to keep a new Wal-Mart from being built on a wetlands area near Vallejo, California. “Sustainable models for stores like Wal-Mart don’t address the auto-centric nature of the big-box phenomenon,” says Feller. Instead of a Wal-Mart, his group would prefer to see smaller, local businesses starting up there. “Around one inlet of the slough, we’d allow sustainable businesses, like grocery stores, a church, a restaurant, and dense housing that would allow people to do a variety of shopping by walking. The only thing that doesn’t fit is a supercenter. With an average of 70,000 car trips a week to supercenters, it’s a much more intense use of the land,” he explains.

Because large retailers aren’t likely to go extinct any time soon, some people are more optimistic about big boxes’ effort to lessen their impact. Mike Schade, PVC campaign coordinator for the Center for Health, Environment and Justice, spends his days working with mega-retailers to phase out PVC- and phthalate-filled products (not what you want in a baby bottle) and has thus far convinced Wal-Mart, Target, and Toys “R” Us to ban the toxins from their shelves (Ikea’s been doing it for more than ten years). “The federal regulatory system is broken and outdated,” says Schade. “But retailers have the power to shift entire markets away from products that are harmful to people and the environment by demanding such from suppliers.” So if they’re going green, there is some chance of shifting environmental initiatives in a way that the small drugstore down the street simply cannot. In other words, when Wal-Mart whispers, its suppliers listen.

Goods on the shelves already reflect a greener disposition. Target offers products like recycled rubber doormats, corn-based packaging, and organic clothing. Ikea uses certified wood, sells only unbleached linens, and has a CFL-recycling program. Wal-Mart intends to reduce packaging by 5 percent over the next five years, meaning that things like laundry detergent will only be sold as a superconcentrated liquid, cutting down on bottle size, transportation costs, and plastic.

Ultimately, it’s the national drive to buy that keeps the big-box stores in business and our planet increasingly overburdened. “We need less stuff,” states Phil Tucker, project director for the California Healthy Communities Network. “We’re a nation of consumers, but we can only consume so much before we’ve consumed it all.”

In other words, if you truly want to act sustainably, put down your credit card and go take a walk.