Introducing new radio services or enhancing current ones is dependent on the ability of the service to coexist with other services. Introduction of digital TV must also respect other services and international agreements concerning the use of spectrum. In some countries digital terrestrial TV will be introduced as improvements to existing services, and new spectrum is not likely to be made available. This may even be true where the digital TV system is used for new services, because TV broadcasting is seen by many regulators as spectrum-inefficient and because no free spectrum is available. As a consequence, we have to face the fact that digital terrestrial TV must be able to coexist with present TV services in shared bands. This article discusses the questions related to introduction of digital terrestrial TV and, in particular, the possible trade-offs that will be necessary to make the service work. Will we accept slightly reduced quality in the analog service? What is the noise figure of new receivers? Should it be scalable? Can it be portable? What is the power range? Can it use adjacent channels ? Other questions should be: Is a worldwide scenario possible? Are the constraints the same all over the world? Are the trade-offs equally acceptable anywhere? Yet another will ask if one modulation scheme is superior to another, and must it carry HDTV from the start or would standard or enhanced definition do? There are questions about coverage, graceful degradation, service availability, and so on. Factors affecting the planning process are also discussed.