In the agricultural production systems weeds represent a very important agronomic component, since they cause significant economic losses to the primary sector of the country. Undoubtedly, the first step to design an adequate, effective and appropriate weed management is to a make correct weed identification. The weed identification in field not always is an easy task, being adult stages less complicated than seedlings. It is imperative to point out that when weeds are in the stage of seedlings (3-6 leaves), the more advisable to any action o weed management. A field study was conducted during the period 2015 and 2016, in representative agricultural producing areas of Panama republic with the objective of determining the main phenotypical characteristics of weed seedlings. The survey embraced the identification of 64 species: 32 monocotyledonous grouped in six botany families y 32 dicotyledonous grouped in 16. A technical guide (2018) was published, titled “Common weed seedlings of Panama”, with illustrated color photos and explained text for each specie.