Specific properties of MANETs results in basic differences between wired networks and wireless networks in security solutions. In recent years, trust models have established themselves as a main approach for security and performance improvement of sections of MANETs. Recent researches have used trust models for problems like routing, admission control and information sharing in MANETs. In spite of the considerable studies in this area, there remain several issues and challenges yet to be investigated. These include issues such as concern about application field of network, context and situations of network and the adaptability of trust models in various cases, all of which motivated the present study. In the first step a number of criteria were derived considering the inherent properties of trust and MANETs. Based on these criteria two trust levels with a variety of properties and behavior were introduced. Each level was useful for particular applications and situations. Next, Adaptive Multi Level Trust model called AMLeT was proposed using two complementary trust levels. AMLeT calculates trust in one level of hard or soft and updates calculated trust considering network field, modifications of context and situations with the passing of the time. AMLeT is extensible for different fields of network, applications and situations. Finally, in order to investigate AMLeT's performance and utility, AMLeT based AODV routing was improved. It was subject to evaluation with simulation tool. The results of simulation indicated overall improvement in the network performance without imposing particular overhead time in network operations.