Dundalk and Shamrock Rovers have both been busy in the transfer market.
The title rivals have used the SSE Airtricity League's mid-season break to strengthen their squads ahead of Friday's crucial clash in Tallaght.
Dundalk are five points clear on 49 points after 21 matches, and have won 10 of their last 11 Premier Division matches.
However, there is a long way to go, and a win for the Hoops on home soil on Friday could swing the momentum in their favour.
The Lilywhites have re-signed Andy Boyle after the defender was released from Preston.
Boyle, 28, was a key player for the Louth club during their famous European run, and formed an excellent partnership with club captain Brian Gartland at the heart of the Dundalk defence.
"Dundalk has always had a special place in my heart," Boyle told Independent.ie, revealing he turned down offers to stay in the UK.
"I've got a chance to come home and play the style of football I'm accustomed to. This feels right to me. With the quality of players at Dundalk, we have a chance at another European run."
Rovers have also made some impressive acquisitions.
Stephen Bradley's title challengers have signed UCD duo Gary O'Neill and Neil Farrugia, as well as Cork City striker Graham Cummins in a deal which saw Joel Costrain move in the opposite direction.
O'Neill, 24, has impressed in midfield for UCD since joining the students in 2015.
Farrugia has been linked with a host of English clubs, but the Republic of Ireland U21 international has opted to stay in Ireland to complete his university degree.
Rovers fans will be excited to see the 20-year-old - who is one of the brightest domestic prospects - on the wing for the Tallaght club.
31-year-old striker Cummins will offer the Hoops greater depth in attack following his somewhat surprise move to the capital.
Cummins has scored four goals this season, and notched 18 last year after returning to the Leesiders from England.
Vinny Perth and Stephen Bradley will be hoping their forays into the transfer market give their respective teams the edge in the second half of the season, and these signings were likely made with the upcoming European campaigns in mind.
Elsewhere in the top flight, Izzy Akinade has left Waterford United to return to Nigeria.