It is important to emphasize that not every easement restricting the future development of property will meet the tax law requirements. The tax law requires that the gift be "for conservation purposes." As a rule, the following generalization works: the more significant the land is, the more it adds to the public good, the more likely it is that you will qualify for the deduction. If you are protecting a large tract of primarily undeveloped property or ranchland or farmland, or a smaller parcel of land with scenic or open space qualities, if you are protecting habitat for an important or threatened animal or plant species, if you are preserving a scenic view on a long stretch of roadside that is threatened with subdivision, if you are contributing to a greenbelt around a city or preserving a watershed by a scenic brook or river or lake, your donation is more likely to qualify for a deduction. In addition, you can meet the "conservation purposes" test if you protect important historic property.
You will probably not qualify for a deduction if there is nothing special or unusual about the land that you are protecting except that it does not currently have more houses on it. Think of it this way. If you are truly contributing something to the general environmental well-being of the area, then that's a good (and deductible) gift. If you are truly trying to get away with something ("maybe I can get a deduction for not permitting any more development on my suburban house lot"), and there is nothing particularly unusual about your property or its setting, you are probably not entitled to an income tax deduction. (As a practical matter, in this latter case, it may be difficult to find a donee organization to accept your easement gift. see Local & National Regulatory Resources.)
In many communities around the country, local tax-exempt organizations have been formed precisely for the purpose of protecting open space and other important land in the area. These organizations, often called "land trusts," should be in a good position to assist you.
One final important point about a conservation easement. In many cases it will be possible to qualify for an income tax deduction by giving up the right to develop your property to the maximum possible extent while still retaining the right to do some limited development in the future. If a conservation easement preventing any further development on John and Mary Landowner's Riverview would qualify for an income tax deduction, John and Mary could also reserve the right to build, for example, four more houses on Riverview, subject to certain restrictions and limitations, and still qualify for an income tax deduction as long as the property's conservation values continued to be preserved. Remember, however, that in many cases conservation values and any further development will be incompatible.