On 27 November 1895, Alfred Nobel signed his last will and testament, giving the largest share of his fortune to a series of prizes in Physics, Chemistry, Physiology or Medicine, Literature and Peace – the Nobel Prizes.*   (The Prize for Economics was added 73 years later.)  

* From Reference A below.

NOT included in that list of prizes, however, is the field of mathematics.
For a long time, I believed (and shared) the anecdote that the reason for this was that Alfred Nobel did not get along – even had a feud with a Swedish mathematician Gosta Mittag-Lefler.  For awhile – but not nearly as long – I also shared the commonly circulated story that the reason for the dislike was that Mittag-Lefler may have been involved in a non-mathematical ‘triangle’ with Nobel’s wife! 🙂
So, the story goes, he asked his advisors if there was any chance Mittag-Leffler could win a prize in Mathematics if that subject was included.  His advisors conceded this was possible, so Nobel was supposed to have said “let there be no Nobel Prize in mathematics then!”
It’s a great anecdote, but . . . a)  the “Nobel’s wife” juicy tidbit was debunked fairly early on (at least for me), and b) more recently, the whole story of a ‘rivalry’ between the two has also lost credence. Many historians now believe that the more-probable-but-not-conclusive reason for not selecting mathematics for a Nobel prize is that Nobel simply wasn’t very interested in the subject (like many subscribers? :-)) and didn’t grasp the practical benefits to the world of advanced mathematics.**
It’s a shame when history ruins a good story, eh??

** From Reference C below.

Related Notes 

1.  Nobel is said to have started the prizes to help mitigate his perception as a ‘mechant of death’ due to his invention of dynamite.   (Indeed, his obituary in a French newspaper read “Dr. Alfred Nobel, who became rich by finding ways to kill more people faster than ever before, died yesterday.”)  This would certainly explain his inclusion of the Prize for Peace.   See Reference C for more information.
2.  Mittag-Leffler was actually on the Nobel Prize Committee in 1903, and – thanks to his views of gender equality – was largely responsible for Madam Curie receiving the prize that year with her husband Pierre.   See Reference B.
3.  Mathematicians now have their own “Nobel Prize” of sorts – the Fields Medal.  It is highly prestigious in the math research world, but unlike the Nobel Prize, the award generally goes to young mathematicians.  It’s most rare to have a winner over 40.

References and More Information

A)  For more general information on the Nobel Prize and its recipients, see Nobel Prize Facts. 
B)  For more (fascinating) information on Mittag-Leffler, see Mittag-Leffler 
C) For more information on Nobel’s decisions to award prizes and/or his reasons for not including math, see Nobel & Nobel Prize.