This study deals with the post-glacial deposits in the Fenland basin of East Anglia. During the last 200-300 yrs. artificial drainage has caused the surface level of the peat to fall by about 10 ft. This is due rather to surface peat wastage than to shrinkage or compression. The forest successions in order from the base upward are: (1) oak, (2) oak-yew, (3) pine, (4) pine, (5) alder-willow-sallow. In the center of Wood Fen, tree-pollen analysis confirms this forest sequence. Non-tree pollen and other micro-fossils are used as indices to the past development of the fen. Remains of sphagna are abundant and it is suggested that the forests have the character of "Zwischenmoorwalder." Acid peats have developed above alkaline topogenous peat. The development of peats agrees with a sequence of conditions: (1) of stability or elevation, (2) of submergence (coinciding in the neighboring fens with the deposition of semi-marine clay), (3) of stability or re-elevation, (4) of subsidence (or possibly increased rainfall). The pine forests are post-Boreal, possibly correlated with the Bronze Age. The value of the pollen-analytic method for correlation of the fen peats is bound up with the recognition that local fen woods greatly influence the form of local pollen-diagrams, and it is thus necessary to work out the phases of bog formation and development for each area studied, and to interpret the pollen diagrams in the light of these results. Fen development may be controlled by 3 major factors acting either singly or together: (1) the natural processes of vegetational succession, (2) edaphic and topographic effects such as those produced by relative movements of land and sea, (3) climatic change, especially in regard to temp, and rainfall. The history of fenland development can be satisfactorily developed, whatever technical methods are employed, only by analysis in terms of the operation of these causative factors.