You can come in Paris with either by plane (landing in Orly which is the closest airport) or train (Gare de Lyon).
From Orly (ORY): take the orlyval automatic train to Antony and transfer to the RER B line southwest-bound. You may take any train bound to Saint-Remy-Les-Chevreuse or Orsay-ville. Tickets have to be bought for the final destination prior taking the automatic Orlyval train (it is not a free connection).
Form Paris-Gare de Lyon: take RER A (bound for Cergy, Saint-Germain, Poissy, Nanterre) or Line 14 to Châtelet Les Halles (westbound) and connect to RER -B line southwest-bound. You may take any train bound to Saint-Remy-Les-Chevreuse or Orsay-ville. Tickets have to be bought for the final destination prior taking the metro line 14 or RER-A line.
Your final destination is Orsay Ville. Note that you have to buy tickets for this final destination and not a simple "T" tickets only valid within Paris city or for the metro lines or buses.
In case the RER trains are overcrowded do not hesitate to take trains bound for Massy-Palaiseau and change for a train bound for Orsay-Ville or Saint-Remy-Les-Chevreuses.
The path from Orsay Ville station to LAL is given here: https://drive.google.com/open?id=10NS5k0eq_7KVue0Rf937lG_o_-f-8u5a&usp=sharing where locations of meeting room, LAL team offices and main entrance are given.
