The conservation easement (called a "conservation restriction" in some states) is written up in a legal agreement that is tailored to protect the land's conservation values and meet the financial and personal needs of the landowner. An easement on property containing rare wildlife habitat, might prohibit development of any kind, for example while one on a farm might allow continued farming and the building of additional agricultural structures.
In some cases, a conservation easement may apply to just a portion of the property, leaving the option of development open for the remaining part. It may allow limited building within the area under the easement.
The land trust takes on the responsibility and legal right to enforce the easement. If a future owner or someone else violates the easement - perhaps by erecting a building the easement doesn't allow - the land trust will work to have the violation corrected. (The land trust usually asks for a donation from the easement donor to help offset the cost of future stewardship expenses.)

Are there financial benefits?
If you donate a conservation easement that meets federal tax code requirements, the value of the easement can be treated as a charitable gift and deducted from income tax (to the extent your particular tax situation allows). For income tax purposes, the value of the easement is the difference between the land's value with the easement and its value without the easement. For instance, if a property is worth $500,000 unrestricted, for example, and an easement that precludes further development is placed on it that drops its value to $200,000, the value of the donation is $300,000. Easement values vary greatly; in general, the highest easement values result from very restrictive conservation easements on tracts of developable open space under intense development pressure.
In order to qualify as a charitable donation, an easement must meet federal tax code requirements - in essence, it must provide public benefit by permanently protecting important conservation resources. However, an easement does not have to cover all of the property, preclude all use or development, or allow public access to qualify.
Because a conservation easement lowers the property's fair market value, it can also result in lower property taxes.

What about estate taxes?
If you own land with substantial value you may not be able to pass it on intact to your heirs. When you die, your children may find that the federal estate tax - which is based on the land's current fair market value and is levied at rates as high as 55% - is in the hundreds of thousands or millions of dollars. Selling all or part of the land for development may be the only way to pay the estate tax.
But if you place an easement on the land restricting future development, its fair market value will, in most cases, be reduced. When you die, this reduced value will result in lower estate taxes. An easement's effect on estate taxes is usually more important to landowners with sizeable estates and substantial real estate holdings. However today's real estate market can easily push a property's value into a higher tax bracket without the landowner realizing it.
A conservation easement can also be donated by will. It has the same effect on estate taxes as a lifetime donation. You should be sure to negotiate the easement with the land trust before including it in your will; This assures that the organization is willing and able to receive it and that the easement achieves what you want it to.