can you give an example or sample sentence? My feeling would be "strengthen cooperation" means you already have cooperation, but it needs to be stronger & closer, whereas "enhance cooperation" means you hardly have any cooperation and need to do more of it. eg... The US needs to strengthen cooperation at home and abroad. (We already have cooperative ties, but they are weak and we need to improve them) The US needs to enhance cooperation at home and abroad. (We have very few agreements/partnerships/relationships so we need to make more) I'm not sure everyone would agree with my distinction; it is VERY subtle. Also normally strengthen cooperation is usually separated by "our" "their" "overall" or some other descriptive term. On a side note, I just googled these 2 phrases. "Enhance cooperation" seems to be written by NATIVE English publications far more often than "Strengthen cooperation," which is frequently used by publications from non-native English-speaking countries.