Recent unprecedented changes in agricultural practices have caused the loss of numerous aquatic habitats throughout the British lowlands. On the other hand, water supply schemes and increased gravel and clay extraction have produced many new water bodies. The effects of these activities on the British odonate fauna are discussed. Since 1950, Coenagrion scitulum (Ramò.), C. armatum (Charp.) and Oxygastra curtisi (Dale) have almost certainly become extinct. Populations of Lestes dryas Kirby, Aeshna isosceles (Mull.) and Sympetrum sanguineum (Mull.) have become much reduced; the first two are now very rare insects. Orthetrum cancellatum (L.) and Aeshna mixta Latr. appear to be increasing. – National Nature Reserves in Britain are selected as representatives of habitat types rather than to protect particular species, nevertheless 32 out of the 41 species breeding regularly in 1950 now occur in these reserves. 3 other species are protected in reserves managed by voluntary conservation bodies and 2 others in the state-owned New Forest. – The scheduling of the Hampshire locality of O. curtisi as a ’’Site of Special Scientific Interest” failed to prevent its extinction through the pollution of its habitat. – The value of several nature reserves for dragonflies has been increased by making new ponds. Populations of local species such as Leucorrhinia dubia (Vander L.), and S. sanguineum have been increased, and Coenagrion mercuriale (Charp.) was encouraged to colonise a reserve where it was previously absent by these means. – The Nature Conservancy Council is undertaking experiments with the aim of reintroducing species into the Fens which have become extinct there in recent years.