In 2004, the Asian Development Bank (ADB) updated the sector and thematic classification and identified irrigation and drainage (ID) as one of the subsectors under the agriculture and natural resources sector. ID projects had previously been clustered with rural development projects. Based on the 120 projects rated at the end of 2005, this group had a success rate of 56%. The ID subgroup had a success rate of 55%. ADB has provided loans totaling $4.1 billion for 105 ID projects in 18 developing member countries. This represents 4% of the total ADB loan portfolio and 26% of ADB loans to the agriculture and natural resources sector. The ID projects have been supported by 151 technical assistance (TA) activities amounting to $66.4 million. Bangladesh, Indonesia, and Pakistan have been the main recipients of this assistance, receiving 74% of ID loans and 49% of ID-related TAs. Given that the success rates of ID projects are significantly lower than in other sectors, it is particularly important for ADB to learn lessons that result in successful ID projects.