Around 200 new train services, equating to an extra 20,000 seats per day, will be introduced throughout Scotland in a major rail services upgrade.
Transport minister Derek Mackay has revealed details of a "revolution in rail", which will deliver the largest programme of benefits to rail passengers seen in a generation.
Passengers across Tayside, Stirlingshire, Perthshire, Aberdeenshire and the Borders are set to benefit.
ScotRail currently runs 2300 services per day.
The Scottish Government has decided to retain 13 Class 170 diesel trains, which means 39 additional carriages, beyond the terms of their current leases, which were due to end on 2018.
It says the extra trains create the capacity to make timetable service improvements and it has worked with local stakeholders to decide which services need the extra seats most.
Commuter services between Scottish cities will also run more frequently.
More services are expected to be announced for Tayside, Stirlingshire, Perthsire and Aberdeenshire from 2018.
There will also be increased peak capacity across Fife and the Borders, relieving some of the pressure on commuter services, along with more commuter options linking local towns between Glasgow and Edinburgh via Cumbernauld and Falkirk.
The transport minister said: "We have initiated a revolution in rail services across Scotland.
"From 2018 passengers will benefit from more seats, more services and faster journey times as a direct result of the increased funding that we are putting into the rail network.
"The retention of these units will complement the arrival of our new high speed trains, which will allow for new and improved intercity connections.
"They will also make our rail network more resilient, creating opportunities to run faster services on key commuter routes and offering better connectivity for regional areas."
Phil Verster, managing director of Abellio ScotRail, which operates the services, said: "This is a really significant moment in our mission to transform Scotlands railway.
"In three years time, the service that we provide to our customers will be unrecognisable. Our new electric fleet will be running between Glasgow and Edinburgh, our high speed trains will be linking our seven cities and, thanks to this announcement today, we will have hundreds more services and thousands more seats available to customers across Scotland, particularly in Aberdeen, the north east and Fife."
Liberal Democrat MSP Tavish Scott raised concerns about the age of the rolling stock that will be used for some of the services.
He said: "People in the north and north-east will want some strong guarantees about the 40-year-old rolling stock that will be used for their connections to the central belt. People will be concerned that the Scottish Government is treating the north as second class.
"Reliability issues have plagued travellers in south-west England on these trains for a decade. Passengers describe the trains as providing 'third world cattle truck conditions'.
"Travellers will want to know that these 40-year-old trains have had more than a paint job before being put to work in Scotland."
Scottish Green transport spokeswoman Sarah Beattie-Smith branded the changes "timid".
Ms Beattie-Smith, the lead Green candidate for the South of Scotland region, said: "The SNP seems to think that tinkering with train service numbers is enough to fix Scotland's broken public transport system.
"Don't get me wrong - new rail services are all well and good, but this policy falls far short from the 'rail revolution' the Scottish Government wants to brand it as.
"To properly support the people who are currently isolated by our poor and expensive public transport, we need to do much, much more."
