One of the biggest areas of change in real estate in the past 20 or so years is the widespread acceptance of the condominium as a legitimate form of real estate ownership. From empty nesters to first-time buyers to almost everyone in between, the options offered by condos have attracted buyers.

However, there still is confusion over the difference between a condominium and a townhome. To make matters worse, there is a different form of ownership in some other parts of the country called a "co-op."

So exactly what are the differences in these three forms of real estate, and why are those differences important?

That is the topic of a new book by real estate developer Mark Weiss called "Condos, Co-ops, and Townhomes: A Complete Guide to Finding, Buying, Maintaining, and Enjoying Your New Home." The book is published by Dearborn Trade and is available for $18.95 in stores.

The author begins with a few basic definitions that I think are critically important:

A condominium, or "condo," is a system of ownership of individual units in a multiunit structure combined with joint ownership of commonly used property such as sidewalks, hallways and stairs.

A cooperative, or "co-op," is housing in which each tenant is a shareholder in the corporation that owns the building.

In marked contrast to the first two, a "townhouse" is a style of construction. It is a dwelling, usually with two or more floors, attached to other similar units by common walls.

So what's the difference? A lot! When buying a condo, you are truly buying real estate -- solid property that you can touch, such as walls, floors and ceilings -- but you are not purchasing the land. In addition, you are buying an "undivided interest" in common areas like the parking lot, the land under the buildings and maybe the pool, if there is one.

But when you buy a co-op, you are not buying land or property. Instead, you are buying shares in a company just as if you were buying Coca-Cola or Home Depot stock or shares in any other private company. You may live on the property, but you really don't own the roof over your head or the dirt under your feet.

Taxes are paid by the property owner, which is usually the corporation, and this expense is passed on as part of your rent.

As a corporation, a co-op has a board of directors with the power to approve or reject potential investors according to the individual's or family's income level or personal character.

So condos and co-ops are forms of ownership, each offering various levels of control and regulation, while a townhouse is, in fact, simply a style of construction.

Thus, while it would be impossible to distinguish a condo form of ownership from a co-op just by driving past the building, a townhouse would be easily identifiable just by looking at it.

A set of attached townhouses might be owned as a condominium or even as a co-op. However, many townhomes in the Atlanta area have been set up under a "fee simple" form of ownership even though they may have common walls.

"Fee simple" ownership is the most common form of ownership in which you own everything associated with the property, including the structure and the land.

In his book, Weiss goes into detail covering the pros and cons of each form of ownership as well as considerations that should be given to the various styles of construction commonly encountered in condos and co-ops.

The vast majority of common ownership developments in Georgia are set up under the Georgia Condominium Act, making them condos. In contrast, the laws of New York favor development under the "co-op" form, so most apartment-style buildings we see on "Seinfeld" are actually owned as "co-op" units.

Benefits provided by condos and co-ops that are covered in the book include:

• Affordability: Because the developer can get a higher density of unit per acre of land, the unit cost of each dwelling can be more affordable, thus making ownership possible for more people.

• Location: Because the developer can spread the cost of acquiring the land over many units, a buyer can hope to live in a better location in a condo than he might ever be able to afford in a detached single-family home.

• Amenities: How else can a first-time buyer expect to buy a home with a pool, a gym, a clubhouse and, perhaps, a doorman?

• Economies of scale: It is theoretically more efficient for the association to hire one person to mow the lawn than for 100 owners to mow their own land.

John Adams is a broker and investor. He hosts the "John Adams Radio Show," a call-in program dealing with homeownership and real estate, from 1 to 3 p.m. Saturdays on NewsRadio 640 (WGST). For more real estate information or to make a comment, visit www.money99.com.