From the MTA, a timeline of milestones:

2015 - February - Contract CM014B is awarded. The contract will complete the architectural, structural, mechanical, and electrical facilities that will comprise the new LIRR concourse at Grand Central Terminal and related ventilation facilities at 44th and 50th Streets.
2014 - September - 50th Street Commons (public open space) opens adjacent to the 50th Street Ventilation Facility.
2014 - September - Contract CM013 50th Street Ventilation Facility completed.
2014 - April - Contract CS179 is awarded to complete the communication systems to be used by the public and employees of the future LIRR concourse.
2014 - April - Second contract (CM006) awarded for the permanent structural concrete linings, interior structures and fit out for the caverns and tunnels north of Madison Yard.
2014 - February - Contract CM013A successfully completed excavation and drill and blast operations at 55th Street.
2013 - November - Contract CH057A is awarded to complete the Westbound Bypass and is the first major construction project to be funded by the Federal Railroad Administration High Speed Intercity Passenger Rail Program.
2013 - September - Contract CM009 Manhattan Tunnels Excavation completed.
2013 - August - First contract awarded for permanent structural concrete lining, interior structures, and fit-out for caverns and tunnels.
2013 - August - Final pile removed at Northern Boulevard tunnel.
2013 - August - The successful conclusion of the summer outage for construction of the track slab to accommodate work on the Westbound Bypass.
2013 - June - Contract CM019 Manhattan Structures Part 1 completed.
2012 - September - Manhattan and Queens tunnels connected.
2012 - July - Queens tunnel boring work is completed. All ESA tunnel boring work ends.
2012 - May -East Side Access completes third Queens tunnel ahead of schedule.
2011 - January - Queens tunnel boring work begins.
2010 - October - Manhattan tunnel boring work is completed.
2008 - May - Preparation work begins in Madison Yard for the new LIRR Concourse.
2007 - September - Manhattan tunnel boring work begins.
2006 - July - Major construction begins in Manhattan.
2006 - April - Major construction begins in Queens.
2006 - December - FTA and MTA sign full funding grant agreement ($2.2 Billion).
2006 - January - ”Amtrak Agreement” signed by LIRR, MTACC and Amtrak.
2003 - July - MTA Capital Construction Company created.
2002 - June - East Side Access enters final design phase.
2001 - March - FTA Approves ESA Environmental Impact Statement.
2000 - May - Draft Environment Impact Study is published, public review and comment period begins.
1998 - September - FTA approves MTA request to enter preliminary engineering.
1998 - Environmental and planning work begins.
1998 - April - Major Investment Study completed, East Side Access project determined to be the best option.
1992-1998 - Major investment and project feasibility studies of east side transportation alternatives are conducted.
1969 - November - 63rd Street Tunnel construction begins.