THIS special section of Transactions on Parallel and Distributed Systems is devoted to middleware infrastructures and gathered nine papers. The first paper is about refactoring middleware with aspects and is authored by C. Zhang and H. Jacobson. The paper is a case for the introduction of aspect-oriented programming techniques within object request brokers. The second paper describes an energy-efficient object discovery protocol for context-sensitive middleware for ubiquitous computing, and is authored by S. Yau and F. Karim. The paper introduces a technique for discovering objects in a distributed environment that is efficient in terms of energy consumption. The third paper describes a middleware platform called OBIWAN, and is authored by P. Ferreira, L. Veiga, and C. Ribeiro. The platform performs automatic creation of object replicas (e.g., incremental on-demand replication) as well as garbage collection of useless objects. The fourth paper presents a middleware infrastructure for parallel and distributed programming models on heterogeneous systems, and is authored by J. Al-Jaroodi, N. Mohamed, H. Jiang, and D. Swanson. The infrastructure handles class loading and distributed deployment in a transparent manner. The fifth paper is about an adaptive quality-of-service aware middleware for replicated services, and is authored by S. Krishnamurthy, W. Sanders, and M. Cukier. The idea is to provide the clients of a replicated service the ability to specify temporal and consistency requirements and have the server adjust its replication strategy according to these requirements. The sixth paper describes an OCI-based group communication support for CORBA, and is authored by D. Lee, D. Nam, H. Youn, and C. Yu. The paper presents a way to transparently enhance CORBA with group communication and object group management primitives. The seventh paper introduces a cluster programming middleware for streamorientedapplications, and is authored by U. Ramachandra, R. Nikhil, J. Rehg, Y. Angelov, A. Paul, S.Adhikari,K.MacKenzie,N.Harel, andK.Knobe.Thepaper presents a middleware infrastructure with adequate support for data abstractions, dynamic cluster-wide threads, data parallelism, and multiple address spaces. Theeighthpaper focuseson thedesignandperformanceof real-time Javamiddleware and is authored byA.Corsaro and D. Schmidt. The paper describes an open-source implementation of the real-time specification for Java middleware and corresponding performance measures. The ninth paper describes clustering support and replication management for scalable network services, and is authored by K. Shen, T. Yang, and L. Chu. The presented middleware infrastructure, named Neptune, employs a loosely connected and functionally symmetric clustering to achieve scalability and robustness. We are extremely grateful to all the reviewers who provided very useful feedback to select the papers and improve their presentation, as well as to all of the authors of the submitted papers for their interest in this special section.