Weeds are problematic both in agricultural and non-agricultural areas so that they potentially cause economic losses. Weed interference in crops also date back to the beginning of agriculture and they have been able to persist, in spite of long term control operations. They are able to adapt and survive in the environment due to their specific characteristics. Thus, to control weeds efficiently knowledge of weed biology, in particular their survival mechanisms, ecological responses and interactions, is of important value in weed management systems. "Weeds and their Ecological Functions" provides information on weeds functional behaviours in their cultivations including weed seed dormancy, germination and seedling emergence, examples of beneficial and detrimental interactions between weeds and other organisms, weed behaviours in perennial crops and response of weeds to cover crops. This information is useful for students and weed scientists to analyse some of the functional behaviour of weeds and to develop integrated weed management systems.