Ok - a great place to start is Carolyn Merchant's textbook, Major Problems in Environmental History. It's a fantastic mix of documents and essays, and to a certain degree also gives you an idea of what directions the field has come from and where it's going.

If you are interested in any specific sub-genre of environmental history I can give you more detailed recommendations - history of environmentalism, history of conservation, enviro-tech, environment and gender, environment and race, urban environmental history, etc. etc. etc.

If you want to start in the places the field started I would go with William Cronnon's Changes in the Land - it's an environmental history of the colonization of New England, and is still excellent, although it has been disputed, revised, and corrected by a variety of historians on points big and small (as happens with any classic work of history over time!).

That's a big question! 'Environmental History' not only encompasses studies about how humans have modified their environment, but also studies of how humans think about and interact with their environment (so, say, the questions 'What is nature'? and 'What does nature mean to us?'). It also leaves a lot open to time period and geographic region.

I can't tell if you're asking for this specific approach to environmental history history because you're interested specifically in it, but the lack of other specific details (era, place) suggests that this is just the one approach you're aware of.

The recommendations that /u/TheShowIsNotTheShow list are all great starting places. But if you want to branch out into other approaches to environmental history other than 'how have humans changed the environment?', here's a few of my favorites:

William Cronon, Nature's Metropolis: Chicago and the Great West

William Cronon, "The Trouble with Wilderness; or,. Getting Back to the Wrong Nature" in Uncommon Ground: Rethinking the Human Place in Nature (you can also find the chapter widely available online).

Bruce Braun, “‘On the raggedy edge of risk’: articulations of race and nature after biology” in Race, Nature, and the Politics of Difference

If you're looking for a less scholarly, more popular audience-oriented work, try Jennifer Price's Flight Maps: Adventures With Nature In Modern America

For those interested in modern German environmental history, I suggest David Blackbourn's fairly recent text, The Conquest of Nature: Water, Landscape, and the Making of Modern Germany (Norton, 2007). I am a gender historian, so this recommendation may not be the best introductory text concerning environmental history and/or Western European narratives detailing the relationship between built and natural environments, per se. That being said, Blackbourn's analysis still offers ample insight into modern German nationalism, territorial conquest, and their intersections with post-eighteenth-century hierarchies of sociopolitical power. I recently read it for a seminar in modern European history, and I found it a surprisingly fascinating insight into a historical subfield that individuals like myself are not necessarily familiar with.