This study examined how internal and external boundary conditions impact the relationship between high-investment human resource systems (HIHRS) and labor productivity in small firms. The study found that: 1) A differentiation strategy negatively moderated the impact of HIHRS on productivity, such that HIHRS decreased productivity more for firms pursuing differentiation. 2) Capital intensity positively moderated the impact, such that HIHRS increased productivity more for capital-intensive firms. 3) Industry dynamism did not moderate the impact as hypothesized. 4) Industry growth positively moderated the impact, such that HIHRS increased productivity more for firms in high-growth industries. The results suggest the impact of