The study of organisational culture and the linkages that it has with both organisational outcomes and national culture is a crucial topic in management literature and a gap in this research was identified in Vietnam. This research took an Explanatory Sequential Mixed Methods approach so that a qualitative stage could verify and explore the quantitative results in the Vietnamese context. The Denison Organizational Culture Survey (DOCS) was used to collect responses from 123 Vietnamese employees to understand the nature of organisational culture in Vietnamese organisations and to predict the relationship with performance using PLS-SEM. The quantitative results informed the development of interview questions for the qualitative stage which then involved interviewing ten Vietnamese employees and categorising their responses using NVivo. The findings showed that traditional Vietnamese cultural characteristics are important in forming the organisational culture in contemporary Vietnamese organisations while contemporary Western management values are also influencing the organisational cultural dynamics. Collectivist and family values were shown to be a key part of Vietnamese organisational culture while more contemporary Western values such as empowerment are seen as increasingly important against a backdrop of continued respect for hierarchies. The strongest drivers of performance are a focus on the mission, and goals and objectives of the organisations supported by the internal focus of teams being well coordinated and aligned in achieving these objectives. An increasing focus on the customer and employee capability development are also important drivers of performance while the nature of organisational culture is internally focussed while demonstrating characteristics of both stability and flexibility. This study contributes to the broader body of research related to organisational culture, organisational performance, and Vietnamese culture and to these areas in the Vietnamese context. It adds to research employing the Denison Model (DM) and contributes to the growing body of mixed methods research in business and in organisational culture and performance studies. The findings add validity to the application of the DM to test these relationships and for the use of PLS-SEM as a tool that demonstrates predictive validity. The research also makes practical contributions to managers in Vietnamese organisations through better understanding organisational culture and the relationships between national culture and performance to allow for more informed managerial decision making in shaping the culture of organisations in Vietnam with an aim of improving performance outcomes.