After a year of landmark deals which are opening new markets for Islamic finance, the industry is under fresh pressure to address some of its shortcomings and prove that it is not just an imitation of conventional finance.
Born in its modern form during the 1970s, Islamic finance has boomed in the last few years on the back of strong economic growth in its core markets, the Gulf and south-east Asia.
Over the past 12 months it has shown signs of going global, as even non-Muslim countries have promoted it in the hope of luring cash-rich Islamic funds. Britain, Hong Kong and South Africa issued debut sovereign Islamic bonds; the industry's world-wide assets are now estimated to total over $2 trillion.
But with this success have come doubts over whether Islamic finance is living up to all of its principles. After all, it was launched not merely to make money, but to promote Muslim values such as equity, risk-sharing and social inclusion.
Those values may sometimes be getting lost as financial institutions engineer products which obey the letter of Islamic law - for example, a ban on interest payments - while mimicking conventional finance in many ways.
Top industry bodies such as the Jeddah-based Islamic Development Bank, a multilateral lending institution with 56 member countries, are leading calls for Islamic banks to strengthen their moral foundations and promote real economic activity instead of monetary speculation.
This will require the sector to go back to the drawing board and develop genuine Islamic finance products that are not only profitable but support socio-economic development, IDB president Ahmad Mohamed Ali said in a speech in Jakarta in November.
"The potential of Islamic finance is not fully realised and in practice most financing is concentrated on a few modes."
A survey by consultancy PWC, published last October, found only 52 percent of Islamic banking customers in the Gulf region believed their bank lived up to their religious values.
Ashruff Jamal, PWC's global Islamic financial services leader, said Islamic banks were "at a crossroads" as growth was slowing and to maintain expansion, they would need to convince increasingly sophisticated customers that they were different from conventional banks.
One area of controversy is the structures which Islamic banks used for funding. In Asia and parts of the Gulf, for example, murabaha - a cost-plus-profit deal where one party buys merchandise for another - is popular. But scholars criticise it for its resemblance to a conventional loan, with the pricing of a murabaha contract effectively acting as an interest payment.
Structures with stronger risk- and profit-sharing elements such as musharaka, a partnership in which two or more parties agree to provide capital, are rarer.
In some jurisdictions, regulators are moving to change this, but it remains to be seen whether they can shift entrenched behaviour among the banks.
In Pakistan, central bank governor Ashraf Wathra warned Islamic banks last week to develop ways to reward their customers in line with a rise in the sector's profitability, or face unspecified regulatory action.
In Malaysia, the government plans to roll out an investment platform this year to spur wider use of risk-sharing and equity-based contracts by Islamic banks.
The result of such initiatives could be to push Islamic banks beyond their longstanding role as credit providers to become investment intermediaries - a shift that would bring them closer to the spirit of Islamic finance, some analysts feel.
"Banks will become more of a full-service, asset manager-type of organisation versus just banking services," said Khalid Howladar, Moody's global head of Islamic finance.
Also controversial are the "Islamic windows" of banks and insurers, which let them operate conventional and sharia-compliant businesses side by side. Funding of the two sides is supposed to be completely separate, but the arrangement can lead to doubts.
Although Islamic windows are common, they can make it hard for Islamic institutions to distinguish themselves from conventional ones in the eyes of consumers, PWC's Jamal said.
There are signs of a gradual regulatory backlash against the practice. Qatar banned it in 2011, and when Oman introduced Islamic banking rules in 2012, it required Islamic windows to operate out of physically separate branches. In Indonesia, a new law requires insurers to spin off their Islamic windows by 2024.
It may be harder, though, to ensure Islamic finance lives up to the principle that it should promote social welfare by giving needy people better access to funds.
Tens of millions of people in the Muslim world lack bank accounts because of poverty, poor education and lack of infrastructure. In theory, Islamic banks could help to change this by attracting customers who are not served by conventional banks. But outside a few areas, such as rural Afghanistan, there is little evidence of them doing this on a large scale.
"At the moment this has been neglected, so there is a void - this is not in line with Islamic teaching," said Abdul Halim Ismail, who in 1983 founded Malaysia's Bank Islam, the country's first full-fledged Islamic lender.
Ismail is prompting the idea of an institution that would channel charitable funds into projects to help the poor and needy, with such investments managed by Islamic banks to burnish their social credentials.
But few Islamic banks - perhaps inevitably, given pressure from shareholders and financial markets - are embracing the social dimension and making substantial efforts to offer products such as sharia-compliant microfinance.
Excluding some efforts in Indonesia and Pakistan, "I fear there is not much to tell regarding an attempt by bigger Islamic finance institutions to become active in microfinance," said Matthias Range, advisor at the German government's international development agency GIZ, which supports such efforts.