The Knowledge Development Box (KDB) introduced in Ireland offers an effective tax rate of 6.25% on qualifying profits from R&D activities focused on patents and copyrighted software. It provides incentives for companies to conduct R&D in Ireland and allows for the interaction with other tax reliefs, such as the R&D tax credit. The KDB regime is designed to align with modified nexus rules set by OECD, promoting a sustainable tax environment for various businesses.