Marketing departments can be organised in several ways - by function, by geography, by product or brand, and by market or customer - and the question asks which is the commonest.

The most common form is functional organisation. Here the department is divided according to the marketing activities to be performed, with specialists heading advertising and sales promotion, sales, marketing research, new product development and customer service, all reporting to a marketing head who coordinates them. Its popularity comes from its simplicity: it is administratively straightforward, avoids duplication of effort, and allows each specialist to develop deep expertise in one activity.

Geographic organisation adds a territorial layer to the sales force and suits companies selling nationally across varied regions. Product or brand management organisation, which places a manager in charge of each product line or brand, becomes necessary when a company has many diverse products, none of which would receive enough attention in a purely functional structure. Market or customer management organisation is adopted when different customer groups have distinctly different buying habits and needs. Each of these is a response to a particular complication, whereas the functional form is the basic and most widely used arrangement.

Hence the most common form of organising the marketing department is based on functions.