Purpose: The purpose of this research is to explore core contributions from two different approaches to complexity management in organisations aiming to improve their sustainability,: the Viable Systems Model (VSM), and the Complex Adaptive Systems (CAS). It is proposed to perform this by summarising the main insights each approach offers to understanding organisational transformations aiming to improve sustainability; and by presenting examples of applied research on each case and reflecting on the learning emerging from them. Design/methodology/approach: An action science approach was followed: the conceptual framework used in each case was first presented, which then illustrates its application through a case study; at the first one the VSM framework supports an organisational transformation towards sustainability in a community; the second one is a quantitative case study of intended greening of two firms in the supermarket industry, taken from a CAS perspective. The learning from each case study on how they support/explain organisational learning in transformations towards more sustainable organisations was illustrated. Findings: It was found that the VSM and the CAS approaches offer internally consistent and complementary insights to address issues of self-organisation and adaptive management for sustainability improvement: while CAS explains empowerment of bottom-up learning processes in organisations, VSM enables a learning context where self-organised networks can co-evolve for improved sustainability. Research limitations/implications: The main aspects of both theories and examples of their explanatory power to support learning in practical applications in organisations were introduced. The initial findings indicate that it will be worth studying in greater depth the contributions to organisational learning from both conceptual models and more widely comparing their applications and insights. Practical implications: The paper offers some guidance to both researchers and practitioners interested in using complex systems theories in action research-oriented projects, regarding the usability and applicability of both approaches. Originality/value: It is considered that, by better understanding organisational ability to adapt and self-regulate on crucial issues for sustainability, it may help to develop one path through the ongoing socio-ecological crisis. While much has been written about sustainability initiatives and governance from conventional perspectives, much less is known about how a complex systems framework may help to address one's pressing sustainability needs. These issues from two innovative complexity approaches as well as the value of using them in action research were illustrated. (Contains 1 note, 1 figure and 2 tables.)