Recorded in late 2014 at Rockfield Studios in Monmouth, Wales, it was produced by the band's lead guitarist Luke Morley and released internationally by earMusic in February 2015.

After breaking up for a second time in 2009, Thunder returned occasionally for a number of shows between 2011 and 2014, before recording a tenth studio album later in the year.

Morley wrote all of the material for the album, with the exception of "Black Water" which was co-written by Saint Jude vocalist Lynne Jackaman.

[12] In promotion of Wonder Days, Thunder announced their first three UK arena headline shows for March 2015, with support bands Reef and Tax the Heat.

[24] Reviewing the album for Classic Rock magazine, Malcolm Dome awarded Wonder Days a rating of four out of five stars, describing it as "Classy, fresh and memorable".

[25] Praising the "rigorous, blues-tinged melodic hard rock elements which established the band's reputation in the first place", Dome highlighted the performances of guitarist Luke Morley and vocalist Danny Bowes, and hailed the album as "a massive reminder that class is both timeless and incandescent".