Why monitoring fails -- What makes effective long-term monitoring? -- The problematic, the effective and the ugly : Some case studies -- The upshot : Our general conclusions. Ecologists and managers of natural resources readily acknowledge the importance of long-term monitoring for improved understanding and management of complex environmental systems. Long-term data are crucially important for providing baselines for evaluating environmental change. They are also fundamental for detecting and evaluating changes in ecosystem structure and function, and for evaluating response to disturbances such as climate change or pollution. Countless scientific articles, books, management plans and other documents have been written about the need to conduct long-term monitoring. However, although there have undoubtedly been some highly successful long-term ecological monitoring programs, there is a history of poorly planned and unfocused efforts that are either ineffective or fail completely.