The structure and dynamics of the plasma environment on the sunward side of comet Halley are investigated using measurements during the Vega inbound encounters from a double probe antenna and two Langmuir probes (the APV-V experiment), within a cometocentric distance of ~850,000 km. Based upon the behavior of the electric fields and the cold electrons, three regions can be identified in the cometosheath (in particular during the Vega 1 approach); transition layers are passed through at ~780,000 km (R1) and ~360,000 km (R2). The outer cometosheath (near and beyond R1) is characterized by large-scale variations in the cold electron density and the electric field, peaking at ~1 mHz. The R2 crossing is detected in the plasma wave data as enhanced fluctuations at ~15 mHz. About 25,000 km downstream of R2, the spacecraft traverses a current layer (thickness ~10,000 km) indicated by a sharp gradient in the dc electric field and the cold electron density. The continuous, relatively rapid increase in the intensity of plasma waves begins at a cometocentric distance of ~200,000 km. Simultaneously, the cold electron density starts growing in accordance with the r-2 law. The cometopause crossing at ~160,000 km produces only moderate effects in the APV-V measurements. In the cometary plasma region, some interesting features are examined, such as a current layer passed by Vega 1 at 54,000 km and sudden ion density enhancements observed by Vega 2 at ~35,000 km. On several occasions, the APV-V measurements are heavily influenced by dust particles striking the spacecraft structure. From these events we can conclude that the dust particles are strongly charged and partially coupled to cometary plasmas (or vice versa). ¿1991 American Geophysical Union