Part 1 of 2. The objectives of the study were 1) to systematically assess and characterize postharvest losses for key horticultural crops in four countries using field based measurements at the farm, wholesale and retail markets, to increase the knowledge base and identify priority postharvest problems that currently limit market access for small farmers and rural marketers, 2) to identify and field test postharvest technology options that could solve priority postharvest problems by conducting field trials in Sub-Saharan Africa and South Asia, and 3) to identify postharvest technology interventions that would specifically address the identified priority problems and serve to reduce food and value losses, and that are of appropriate scale, cost effective, easy to use on a trial basis and capable of generating increased incomes by at least 30% for small farmers. A series of comprehensive postharvest assessments were undertaken in Ghana, Rwanda, Benin and India during 2009 to identify the % physical losses, quality changes and economic value of losses for 16 different crops. Based upon these assessments, supplemented by interviews of various players along the value chains, primary causes and sources of postharvest losses and quality problems were identified. Sampling, objective and subjective measurement of physical losses and quality parameters were conducted at the farm, wholesale and retail markets in each of the four countries by trained data collectors housed at 10 partner institutions. Ten (10) random samples were collected at each of the 3 levels of the value chain for each crop. Tomatoes were assessed in all 4 countries, mangoes in 3 countries, and other crops in one or two countries each. Sample sizes and quality parameters varied by crop type. Sorting was done to determine overall quality, % damaged, % decayed and % with other defects within each sample. Rating scales were developed for visually assessing quality, color changes, stage of ripeness, and degree of package protection. Objective measurements of firmness, SSC%, air temperature, pulp temperature and % RH were made using hand held tools in the field. Postharvest losses were related to one or more of 4 major factors: 1) high temperatures, 2) poor quality packages, 3) poor field sanitation and 4) time required to reach the market.