Museums and galleries are places of personal and community fulfilment. They can liberate the imagination, open doors to the past and reflect the creative energy of the present. They are powerful instruments in the fight against what Tessa Jowell, the culture secretary, recently called the "poverty of aspiration".  Success for museums depends above all on the excellence of their collections and the scholarship and care that sustains them; the distinction of their buildings; the creativity of their staff; and the harnessing of resources for the benefit of many different audiences. At a time of limited public funding, ability to generate revenue is vital.  The government rightly expects museums to be cultural, social and economic hubs, and a key educational resource. Astonishingly, given the constraints of recent years, many succeed. We at the Tate contribute to tourism, promoting international dialogue. We are formidable agents of regeneration. Most significantly, we offer a place of illumination and contemplation, in which we can discover our own identity and concerns that bind us together.  At the same time, we are reaching out to the world beyond our doors, cultivating new audiences. Furthermore, because we have stimulated visual awareness, we are welcoming a public that is more critical and expects greater depth and sophistication.  Today, on International Museum Day, we have much to celebrate. The government has kept its promise to make entry free for all nationally funded museums and galleries: the policy has been a huge success, attracting nearly 11 million extra visitors in its first two years.  However, many of the 2,500 museums and galleries in the UK are struggling to maintain the principle of free entry established when the British Museum was founded in 1753. In 2002 the government commissioned Renaissance in the Regions, a report that presented a coherent plan to revive regional museums by investing £267m over five years in nine centres of excellence, which would in turn help smaller local collections; however, the government could come up with only £70m over three years, so the scheme is going ahead in just three regions.  In spite of everything, museums are a success. In 2002 (the latest figures available) six of the top 10 visitor attractions were museums, and more than 6 million children - roughly half of all young people in the UK - visited a museum; 3 million people took part in structured learning activities in museums, with more then 5 million learning off site. Parents consider museums the best learning environments, after schools.  Museums have always had a mission to educate. But over time our museums have been asked to do more and more. They are no longer just storehouses for the nation's treasures. In the 21st century, they are expected to be agents of urban regeneration, international tourist attractions and centres for local communities. They have risen to this challenge. They do everything they can to earn their own keep through trading activities and sponsorship. Overall, they attract 100 million visitors a year, which brings £3bn to the economy.  But the museum economy itself is near breaking point. The success of free entry has placed ever greater demands on resources - at Tate Modern we have even found a sponsor for lavatory paper. With art prices reaching astronomical levels, we are having difficulty in renewing the collections that are at the heart of what we do.  Many of our national museums have international responsibilities, representing Britain in the wider world and attracting audiences to this country. But we are losing ground compared with other European countries - only a few weeks ago, France announced a £30m investment for the Louvre's Islamic collections. We rely on the lottery, now able to give only small capital grants.  Regional museums have to struggle even harder, for there is no legal obligation for a local authority or university to sustain collections inherited from a more expansive and morally responsible era. Few regional museums can now contemplate adding to these collections, and in too many there is a sense of gradual decline as buildings deteriorate and displays age. Valiant efforts are made by curators to build confidence and audiences. But again and again we see examples of institutions that are led by gifted individuals but fail to achieve their potential.  The difficult message for the government is that a further £35m a year is needed if the Renaissance programme is to reach the whole country. Moreover, national museums need £50m to make up for past underfunding and cope with the growth in visitors.  The good news is that a government that has made the great national treasure houses free to all does seem prepared to listen. For the first time, all 2,500 museums have come together to send a single message in their Manifesto for Museums. We hope that the government will find a way to build on success.  · Nicholas Serota is the director of the Tate Gallery
Nicholas Serota: They have never been more popular. So why are many of our museums and galleries beset by pessimism?