Why Bitcoin has value

1. Bitcoin is limited in supply to 21 million, halving inflation every 4 years. Right now it's inflation rate is around 4-8% making it comparable to many 3rd-world economies. As such these countries use Bitcoin as a store of value.
2. Why do they use Bitcoin instead of Gold, USD or Stocks?
   Because Bitcoin is resistant to control, its decentralised, nobody controls it, nobody can confiscate it easily or stop you buying/selling it.
3. It's used as a currency - It is accepted in thousands of brick and mortar locations
   around the world (coinmap will help you visualise this) and many more online including
   some big hitters such as Wordpress, Dell, Microsoft etc.

Those 3 reasons explain why is has value in the first place and what helped to drive the price up to the range 400$ that is has averaged over the last 2-3 years.
So why has it accelerated this year?

1. Inflation recently halved again - this was back in Summer 2016, since then it has been in a stable bull trend

2. It's has become a store of value during crisis, everything from India and Venezuela trying to control the currency markets, to Brexit and Trump
   when investors wanted to put their money somewhere safe.

3. Because of the reasons above major hedge funds and big investors now want Bitcoin as a part of their portofolio, some adopted early such as the Winklevoss Twins,
   Richard Branson etc, however these guys require heave regulation and have had very few easy routes into the market, as a result
   there have been 3 major ETF's filed by huge investment funds, one of which is due for its final decision by March 11th, Analyst expect between 300-500m to enter the Bitcoin market if it gets approved, so smaller investors are trying to take positions early.

4. Bitcoin has hugely disruptive properties from a tech perspective. It's effectively a decentralised almost free to use database, as such it is capable of all kinds of cools things such as smart contracts and coloured coins.