A continuous ink system (CIS), also known as a continuous ink supply system (CISS), a continuous flow system (CFS), an automatic ink refill system (AIRS), a bulk feed ink system (BFIS), or an off-axis ink delivery system (OIDS) is a method for delivering a large volume of liquid ink to a comparatively small inkjet printhead. Many business and professional grade printers incorporate a continuous ink system in their design to increase printing capacity.

Some aftermarket companies also build retrofit accessories to convert certain models of consumer-grade printers into continuous flow systems. Such systems have been frowned upon by most printer manufacturers, as they have been seen as a threat to their business model of selling the printer itself as a loss leader and making their profit off replacement ink cartridges, prompting lawsuits against aftermarket firms or implemented digital rights management measures in their devices (see Razor and blades model). Some manufacturers have introduced new models featuring continuous ink systems. This was seen as a welcome move by users, especially small business owners who rely on bulk-printing solutions, like internet cafes and small-scale print shops.