The theme of this year's International Women's Day is #PledgeForParity. We celebrate the social, economic, cultural and political achievement of women. We look back with pride on our mothers' and grandmothers' achievements, but also focus with anger and determination on the injustices which hold women back today. And we look at the practical measures which are needed to advance the cause of women, not just in Britain but around the world.
And on this day it seems appropriate, given the ongoing debate about Britain's membership of the EU, to reflect on the hard-won rights and freedoms women have achieved through the European Union - and the risks to gender equality inherent in leaving Europe.
Being in Europe means the UK is bound by common rules which ensure protections for women in the workplace, tackle gender discrimination, and fight against income inequality. From maternity leave and work protections during pregnancy, to rules preventing harassment and unequal treatment at work, women in Britain benefit from EU protections every day.
These benefits make a real difference to people's lives - they're not just abstract statistics. This referendum is about the new mum who can spend time with her children without having to give up her job. It's about the cleaner on a zero-hours contact who is freed to go for a scan on work time. And it's about the graduate on her first job who is protected from being paid less by her sexist boss.
Many of us will take these rights for granted. But were we to pull out of Europe, there is no shortage leave campaigners who would like nothing better than to reduce them. Nigel Farage said that working mothers are "worth far less" than men. And the leader of the Vote Leave campaign, Matthew Elliott, called for childcare benefits to be cut by 80% when he led the Tax Payers' Alliance.
Women, just as much as men, are better off in the EU thanks to the jobs our membership creates, the security it delivers, and the action on climate change it pioneers. We know that financial crises and austerity hit women hardest, so the boost that the EU gives our economy matters more to us than it does to men. Similarly cross-border work on tax evasion and financial regulation is crucial for safeguarding us from the dangers of an unregulated market. On climate change, much as the Paris climate agreement does not go far enough, if you listen to representatives from Small Island States - some of the poorest countries with the most to lose from climate change - they'll tell you that working with the EU was key to getting the crucial 1.5 degree climate goal into the final agreement. The deal gives us at least a chance to curb the looming threat of catastrophic climate change.
As feminists, we care about women across the world, not just our country or even our continent. The global fight to end violence against women and gender discrimination is one of the biggest challenges of our time. Being in Europe gives Britain the power to work with our European allies in promoting common values of non-aggression and equality to protect and empower women. To this end, the UK draws on a host of European initiatives to fight for women in Europe and across the world. These include common action to stop sex trafficking, and funding for projects aimed at ending female genital mutilation.
All of us are better off when we work together on the shared challenges we face. Every woman who has taken maternity leave, benefited from anti-discrimination laws, or got a job created by doing business on the continent has the EU to thank, at least in part. It is this that should be at the forefront of our minds - not just on International Women's Day, but on every day from now until 23 June.
Caroline Lucas is the Green MP for Brighton Pavilion