**Abstract**

Port wine is a traditional and worldwide renowned fortified wine produced in the Douro Demarcated Region (DDR) Northeast of Portugal by specific and traditional winemaking practices. The final quality and uniqueness of the different Port wine styles are highly dependent on the ageing process, namely time, temperature and oxygen levels that will ultimately dictate the type and extension of the chemical changes that occur during this process. These chemical changes occurring during the Port wine ageing process results in significant changes in colour and aroma according to the different ageing conditions employed for the different Port wine styles. This chapter intends to give a broad and generic overview of the known and potential chemical changes occurring during ageing of Port wine that are responsible for the changes in the sensory profile observed during the ageing process. Also, the known chromatic and aromatic characteristics of the different Port wine styles and the specific ageing processes, reductive or oxidative, are reviewed.

**Keywords:** Port wine, Douro Demarcated Region, ageing process, colour, aroma
