Abstract: The High Level Architecture (HLA) is a standard developed by the US Department of Defense (DoD), and is meant to establish interoperability among different types of simulations at multiple locations for the simulation of sometimes highly interactive activities. If there are several HLA compliant federates (simulations) that provide simulation at different levels of resolution, then it would be ideal to combine them into one federation so as to provide realistic training to soldiers of different ranks present within the same federation exercise. The issue of multi-resolution simulation systems thus comes into the picture. Aggregation/disaggregation is used to ensure proper interaction between federates of different levels of resolution. This paper explores the problems of the existing module-based approach to the implementation of aggregation/disaggregation in the HLA environment. Two new approaches and their pros and cons are discussed, and one of them is implemented and tested on a simple dual-resolution federation. A sample simulation run of one of the new approaches is also presented.