For an expression that is used more and more by an ever-wider number of people, sustainability is getting harder, not easier to define.I was prompted to this thought by attending the 20th anniversary celebration of the Prince of Wales’s Business and Sustainability Programme at St James’s Palace recently.  I had taken part in the very first of these programmes at Madingley Hall, Cambridge in 1994.  In fact, apart from Jonathan Porritt and Polly Courtice, the indomitable Programme Director and Director of the Cambridge Institute for Sustainability Leadership, I was the only one present who had done so.  The programme was called Business and the Environment then and was concerned largely with environmental pollution and the scarcity of natural resources.  Over the years since then, climate change has become a much more significant issue and the need to address social as well as environmental issues has been widely recognised.  Hence the change in title for the Programme.In this context, it was interesting to compare the issues raised by the speakers that I noted down.  Jonathan Porritt was concerned by the central role, and not always a positive one, big business had taken over the last 20 years in the political arena.  He made the obligatory reference to Thomas Piketty’s recent book, but acknowledged that nevertheless the business community as a whole had made significant strides to embrace sustainability.  Terry A’Hearn, Chief Executive of the Northern Ireland Environment Agency, focused on the need for regulation but referred to his attempts to get companies to go beyond mere compliance to adopting good behaviour.  Philippe Joubert, ex-President of Alstom Power and Chair of the Prince’s EU Corporate Leaders’ Group, saw climate change as the major challenge for business but said that if business was to be able to make the investments needed to deal with it, it needed stable long term policies from the politicians.  Idar Kreutzer, CEO of Finance Norway, spoke of the increasing importance of ESG issues in financial investment. (For those who are not fund managers or pension trustees, ESG stands for environmental, social and governance issues.)  The Prince himself, as always, seemed modestly surprised at the momentum he had succeeded in generating, but felt that the battle was far from over;  the next twenty years would be more difficult than the last twenty years.So is sustainable development still as defined by the Brundtland Commission in 1987:  “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”?  Is it now focused solely on climate change as described by the Stern Report as the greatest market failure ever seen?  Or does it include all the non-financial issues not usually contained within the financial parts of companies’ reports and accounts?  Or is it simply that we all have different ideas about what the “needs of the present” might be?  Over the next few months as Sustainability First approaches its fifteenth anniversary, we shall be exploring these issues in this blog.let us know what you think.Jon BirdAssociate, Sustainability First