Corporate bond issuance was at a two-year high in May, with the A$13.1 billion of bonds issued the highest monthly volume since May 2014. This is almost twice the average monthly issuance of $7.3 billion over the period.National Australia Bank set the tone at the start of the month by raising $3.2 billion for five years. Included in the transaction was $2.9 billion of floating rate notes - the largest single tranche yet seen.NAB was followed towards the end of the month by Westpac, with a $2.3 billion five-year raising. Other benchmark issues through the month ranged in size from $500 million by the Sydney Branch of Bank of China, to $800 million by the International Bank for Reconstruction and Development.The other highlight of the month was the return of non-financial issuers to the market. Up until the start of May only one non-financial issuer had been seen - Korea National Oil Corporation which issued $325 million of bonds in February.AirServices Australia raised $400 million early in the month. AirServices Australia qualifies as a non-financial issuer but whether it qualifies as a true corporate issuer is debatable.There can also be some debate about the qualification of the next to issue, Ford Motor Credit Company LLC. Ford raised $450 million via a global issue, and this follows the $500 million of global bonds the company sold last December.Port of Brisbane finance vehicle, QPH Finance Co Pty Ltd, was next to market and was the first domestic true corporate issuer. The week before last the company sold $250 million of seven-year bonds.  Hyundai Capital Services completed the non-financial issuance for the month by selling a $350 million of five-year bonds.In all, $1.45 billion of non-financial issuance was seen in May and it appears that June will see even more.