This article examines the relationship between ESG activities and firm value, particularly in family-owned firms. It uses data from Korea to analyze how ESG investment interacts with family ownership. The study finds that ESG activities can help mitigate agency problems in family-owned firms, but careful management is needed to maximize firm value. The concept of the marginal effect of ESG is introduced, and a critical threshold of family ownership is identified as essential for increasing firm value through ESG activities. Depending on a firm's position relative to this threshold, strategies for increasing or reducing ESG investment are recommended. The timing of such investment or disinvestment is highlighted as a key strategic consideration. The findings provide practical insights for family-owned firms to make informed decisions on ESG investment, contributing to both their sustainability and the long-term vitality of ESG activities. The article also discusses the debate around ESG activities. While some scholars argue that ESG initiatives may not generate immediate increases in short-term firm value, others believe that ESG activities can lead to effective and transparent management, prevent opportunistic behavior by CEOs, and improve corporate governance. The study emphasizes the importance of identifying which of the three ESG pillars (environmental, social, or governance) has the greatest impact on firm value. Setting criteria for strategic choices for each ESG pillar is essential to prioritize among them and raise firm value. The study highlights the need for guidance on the strategic selection of ESG initiatives to increase firm value, as ESG activities that do not increase firm value can reduce a firm's chances of survival.This article examines the relationship between ESG activities and firm value, particularly in family-owned firms. It uses data from Korea to analyze how ESG investment interacts with family ownership. The study finds that ESG activities can help mitigate agency problems in family-owned firms, but careful management is needed to maximize firm value. The concept of the marginal effect of ESG is introduced, and a critical threshold of family ownership is identified as essential for increasing firm value through ESG activities. Depending on a firm's position relative to this threshold, strategies for increasing or reducing ESG investment are recommended. The timing of such investment or disinvestment is highlighted as a key strategic consideration. The findings provide practical insights for family-owned firms to make informed decisions on ESG investment, contributing to both their sustainability and the long-term vitality of ESG activities. The article also discusses the debate around ESG activities. While some scholars argue that ESG initiatives may not generate immediate increases in short-term firm value, others believe that ESG activities can lead to effective and transparent management, prevent opportunistic behavior by CEOs, and improve corporate governance. The study emphasizes the importance of identifying which of the three ESG pillars (environmental, social, or governance) has the greatest impact on firm value. Setting criteria for strategic choices for each ESG pillar is essential to prioritize among them and raise firm value. The study highlights the need for guidance on the strategic selection of ESG initiatives to increase firm value, as ESG activities that do not increase firm value can reduce a firm's chances of survival.