The EUs Markets in Financial Instruments Directive II (MiFID II) came into effect today and is expected to be one of the final pieces of regulatory reform following the 2008 banking crisis.
Designed to offer greater protection for investors, it is estimated that global banks and asset managers will have spent $2.1bn (£1.5bn) in order to comply with the 1.7 million paragraphs of rules.
City of London Corporation policy chairman, Catherine McGuinness, said the legislation signifies a "watershed moment", and that companies had worked hard to implement the "onerous and complex" changes.
"While they have been a big distraction for firms, I am certain they are well-placed to strengthen their position in the global marketplace," she added.
It is hoped that the regulation will make financial markets more efficient resilient and transparent, increasing the amount of information available to investors while reducing the use of dark pools and OTC trading.
Some of the changes include fund managers having to pay investment banks and brokers directly for analyst research, instead of combining the cost with trading commission.
In addition, local government pension schemes will automatically be categorised as 'retail' clients rather than 'professional' ones, and will therefore not be able to access some fund classes or products.
This is expected to dramatically impact investment strategies, with the Pensions and Lifetime Savings Association (PLSA) publishing a guide outlining the top actions pension schemes need to take in preparation for the regulation.
"Schemes will have to deal with a vast range of changes affecting everything from the way in which research is paid for, to the disclosure of cost and best execution information," PLSA investment and defined benefit policy lead, Caroline Escott, said.
"Although this poses challenges, it also offers an opportunity for in-depth consideration of the value of schemes' fund management services."
This comes after Sacker & Partners LLP identified five key implications of the regulation for pension scheme trustees, arguing that the full impact of the changes is likely to emerge gradually over time.
"MiFID II will significantly change the way financial markets operate," Sacker & Partners LLP partner, Sebastian Reger said. "The most important message for trustees is to get familiar with the changes."