The spread of Invasive Alien Species (IAS) is now recognized as one of the greatest threats to the ecological and economic wellbeing of the planet. These species are causing varying degree of damage to biodivesity and valuable natural and agricultural systems upon which human beings depend. Direct and indirect health effects are increasingly serious and the damage done is often irreversible The effects are exacerbated by global changes and chemical and physical disturbances to species and ecosystem Alien tree species have long been introduced for commercial forestry, agroforestry, erosion control and landscaping. Pakistan has a long history of introduction of foreign plant and animal species The main objective of introduction of exotic forest tree species was to fill the gap between supply and demand of timber, fuel-wood and fodder. Out of 700 alien species 2 forest tree species viz Broussonetia papyrifera, and Prosopis juliflora were recognized as high impact invasive. Eucalyptus camaldulensis is another example highlighting the invasive behaviour. In addition, Robinia pseudoacacia, Ailanthus altissima and Leucaena leucocephala are also aggressive in nature and may pose threat to the local flora and fauna in the future. This paper presents the present status, impact and possible control measures of invasive alien forest tree species.