This paper explicates the theory-practical interface of Climatesmart Agriculture. Climate-smart Agriculture was developed as a suite of tools to improve socio-ecological systems by fundamentally changing the methods and outcomes of farming. The rationale for Climate-smart Agriculture is the urgency of: reducing the impact of agriculture on climate change; improving food security and nutrition, particularly within the Least Developed countries; developing models for planetary sustainability. The theory of Climatesmart Agriculture states—if interventions to mitigate the damages that traditional agricultural systems cause to the environment are adopted and if growers embrace methods and products that adapt to changing environmental conditions, then greater yields and profitability are achieved while ecological systems are protected, ensuring longterm sustainability. Reliable and internally valid data support the generalizability and replicability of this theory. Each tool of Climatesmart Agriculture is characterized by its equivalent tons of carbon sequestered per given area. Additionally, the cost-benefit analyses of mitigation and adaptation are generally significant and positive. The practical implementation of Climate-smart Agriculture is challenged by a broad set of constraints and barriers, which emanate from social, economic, political and agronomic sources. This paper explains the disconnect between the theory of Climate-smart Agriculture and its practical, long-term implementation in Least Developed countries.