Book excerpt: This manual was prepared within the framework of a technical assistance (TA) agreement entitled “Forest Resources Inventory and Establishment of a forest reference level for REDD+ in Nigeria (UTF /NIR/066/NIR (644170)”, to support the implementation of national forest inventory (NFI) in Nigeria. An NFI is a key component of a measurement, reporting and verification (MRV) system which is a requirement of the United Nations Framework Convention on Climate Change (UNFCCC) for the national forest monitoring system to assess anthropogenic forest-related greenhouse gas emissions by sources and removals by sinks. The results of the NFI will be used to support national institutions to address issues of REDD+ and greenhouse gas (GHG) international reporting obligations. It can be also used to review the policy processes to support sustainable forest management at national level.