Bill and Melinda Gates: Major progress ahead for world poor

Bill and Melinda Gates are confident the lives of the world's poorest "will improve faster in the next 15 years than at any other time in history."

The ambitious vision is stated in the Bill and Melinda Gates Foundation 2015 Annual Letter released on Thursday.

The document lays out a series of goals for global progress in sectors ranging from health to education, stressing the importance of access to innovation and sustainable farming development.

But with heightened inequality and global threats to stability such as Ebola and climate change, why is the couple so optimistic for the future? They sat down with Laura Trevelyan to explain as part of the BBC's "A Richer World" series.

For more on the BBC's A Richer World, go to www.bbc.com/richerworld - or join the discussion on Twitter using the hashtag #BBCRicherWorld.