I met Michel Mousel at Sciences Po in the early 1960s. At that time, he chaired the general assembly of Sciences Po students, attached to the UNEF. It was not only a time of union struggles to promote the status of students, but also a time of struggle against the Algerian war, against the use of torture, and for student involvement in overcoming colonialism.

A few years later, he was elected president of the UNEF, an important trade union position in pre-1968 France.

He was an activist within the Parti socialiste unifié (PSU), created on the initiative of Michel Rocard. The PSU, born out of a reaction against the involvement of the French Section of the Workers' International (SFIO) in the Algerian war and out of an unfailing critique of Stalinism, was the matrix of the self-managing left, committed to participatory democracy, citizen engagement, decentralization and the diffusion of power, all ideas found in the philosophy of sustainable development.

After graduating from the École nationale d'administration (ENA), Michel Mousel joined the Forecasting Directorate of the Ministry of Finance, which at the time had the prestige of having designed and implemented national accounting after 1945. The Directorate was the "thinking head" of the Ministry. Those who served there, far from seeking power and a career, were imbued with the collective concern to provide a solid scientific basis for France's economic policy.

There were many bridges between the Directorate of Forecasting, the Commissariat Général au Plan, the Club Jean Moulin, a renowned think tank at the time, and progressive political circles that sought either to modernise the left or to give a more social colouring to Gaullism then in power. Already, shifting position between think tanks, high administration and politics was a common practice.

The 1970s saw the creation of the congrès d’Épinay’s Parti socialiste and the rallying of Michel Rocard in 1974, while Huguette Bouchardeau and then Michel Mousel kept the PSU's small but fertile house alive with men and women of quality and innovative ideas.

After 1981, and two years of no environmental policy, the need was felt to revive the theme of the environment. Michel Mousel became the chief of staff of the new Secretary of State, Huguette Bouchardeau. For the Ministry of the Environment, which had emerged terribly weakened from an unequal merger with the Equipment Department, deprived of resources and without an international service, at a time when international and European environmental policy was taking off, notably with the negotiations on acid rain and the protection of the ozone layer, the arrival of this new team was a welcome opening. In 1985, the Bouchardeau law on the democratisation of public enquiries symbolised the interest in a citizen and participatory approach to planning and environmental issues.

After the appointment of Michel Rocard in 1988 as Prime Minister and Brice Lalonde as Minister of the Environment, whose cabinet I headed, it was quite natural that we thought of Michel Mousel, who had become immersed in environmental issues by enriching them with his vision as an economist, to head the Water and Pollution Prevention Directorate. He showed great brilliance. We owe him the revival of the water agencies, which had suffered greatly from the restriction of their resources. We also owe him an unfailing commitment in the negotiation of the 1991 European Directive on wastewater, which enabled decisive progress to be made in equipping French towns and cities with wastewater treatment plants.

It is once again to him that the government called on to set up and preside over the new Ademe (now Ademe-Agency for Ecological Transition), resulting from the merger of the French Agency for Energy Management (AFME), the National Agency for Waste Recovery and Disposal (ANRED) and the Air Quality Agency (AQA). Merging agencies of different cultures, statuses and means is always a challenge. Michel Mousel put all his administrative and financial know-how, his concern for people and his diplomatic skills into it. Ademe was put on the right track and has since played a major role in sustainable development policies in France.

Michel Mousel adhered unreservedly to the philosophy of sustainable development as expressed in Agenda 21 adopted at the Rio Conference in 1992, which includes many themes dear to its heart, in particular the participation of stakeholders and the links between the economy, social equity and protection of the biosphere. And it is very logical that, after Rio, he endeavoured to mobilise civil society by creating the Association 4D - Dossiers et Débats pour le Développement Durable, which brings together association activists, researchers, experts, trade unionists, civil servants and executives from the private sector to analyse and debate the challenges of sustainable development.

He took up a high-level public position by chairing the Interministerial Mission on the Greenhouse Effect (MIES) between 1997 and 2002, striving to mobilise ministries for the implementation of the Climate Convention and the Kyoto Protocol, with the credibility that his career gave him.

A multifaceted commitment, a straightforward life at the service of a social ideal, an endearing personality steeped in humanism, an authentic activist for the environmental and social cause, an exemplary and inspiring commitment.