Rwanda and Burundi have joined the East African community customs union, which should lead to lower prices, as goods from fellow members are now duty free.
The union is intended to boost economic cooperation between the newcomers and the EAC’s other members – Kenya, Tanzania and Uganda.
It is also seen as another step towards a possible future political federation.
BBC correspondents in both countries say the true test of this move will be how it improves the lives of the poor.
The BBC’s Geoffrey Mutagoma in the Rwandan capital Kigali says there are fears about the future of Rwanda’s already crippled manufacturing industries.
He says manufacturers in the country need to see how the government will strike a balance between keeping local firms alive, while ensuring that consumer prices come down.
While in Burundi citizens are faced with another challenge – understanding what being part of the union means for their country.
The BBC’s Prime Ndikumagenge in Burundi says officials have spent two months throughout the country educating people about the union, how trade will work and explaining the new jargon such as VAT and what free trade is.
But he says most are still ignorant about it. The ministry of finance Burundi informed that it may take as much as three years for citizens to fully understand everything. There are also plans to launch a single currency.