diff --git a/inst/shiny/functions/logging.R b/inst/shiny/functions/logging.R
index 4a13a242c..ce29dedbc 100644
--- a/inst/shiny/functions/logging.R
+++ b/inst/shiny/functions/logging.R
@@ -6,6 +6,14 @@
 #
 # Log levels: TRACE < DEBUG < INFO < SUCCESS < WARN < ERROR
 # Default threshold: INFO (configurable via aNCA_LOG_LEVEL env var).
+#
+# The log captures application-level events only — not raw R console
+# output. Warnings and errors from third-party packages appear only
+# when explicitly caught by tryCatch blocks with log_warn/log_error.
+#
+# The in-memory buffer is exported as session_log.txt in the ZIP
+# download. For a full reference of logged events, see:
+# https://pharmaverse.github.io/aNCA/articles/session_log.html
 
 .log_env <- new.env(parent = emptyenv())
 .log_env$threshold <- "INFO"
diff --git a/inst/shiny/functions/zip-utils.R b/inst/shiny/functions/zip-utils.R
index 54feab18b..8054ec202 100644
--- a/inst/shiny/functions/zip-utils.R
+++ b/inst/shiny/functions/zip-utils.R
@@ -651,10 +651,38 @@ prepare_export_files <- function(target_dir,
 #' @keywords internal
 .export_session_log <- function(target_dir) {
   log_buffer <- get_log_buffer()
+
+  threshold <- .log_env$threshold
+  header <- c(
+    "# aNCA Session Log",
+    "#",
+    "# This file contains application events captured during your session.",
+    "# It records data upload, mapping, NCA settings, parameter selection,",
+    "# slope adjustments, exclusions, calculation results, and exports.",
+    "#",
+    "# Warnings and errors from these operations are included when caught",
+    "# by the application. Unexpected R errors or warnings from third-party",
+    "# packages that are not explicitly handled will NOT appear here.",
+    "#",
+    paste0("# Log level: ", threshold,
+           " (configurable via aNCA_LOG_LEVEL env var)"),
+    paste0("# Levels shown at current threshold: ",
+           paste(names(.LOG_LEVELS)[.LOG_LEVELS >= .LOG_LEVELS[[threshold]]],
+                 collapse = ", ")),
+    "#",
+    "# For a full reference of logged events, see:",
+    "# https://pharmaverse.github.io/aNCA/articles/session_log.html",
+    "#",
+    paste0("# Generated: ", format(Sys.time(), "%Y-%m-%d %H:%M:%S %Z")),
+    "# -------------------------------------------------------------------",
+    ""
+  )
+
   if (length(log_buffer) == 0L) {
     log_buffer <- "(No log entries captured during this session.)"
   }
-  writeLines(log_buffer, file.path(target_dir, "session_log.txt"))
+
+  writeLines(c(header, log_buffer), file.path(target_dir, "session_log.txt"))
 }
 
 #' Clean Export Directory
diff --git a/pkgdown/_pkgdown.yml b/pkgdown/_pkgdown.yml
index 815656825..392b6ecfe 100644
--- a/pkgdown/_pkgdown.yml
+++ b/pkgdown/_pkgdown.yml
@@ -29,6 +29,8 @@ navbar:
           href: articles/adding_tlg.html
         - text: Design & Architecture
           href: articles/design.html
+        - text: Session Log Reference
+          href: articles/session_log.html
         - text: Functions manual
           href: reference/index.html
     project:
diff --git a/vignettes/session_log.Rmd b/vignettes/session_log.Rmd
new file mode 100644
index 000000000..183575b3f
--- /dev/null
+++ b/vignettes/session_log.Rmd
@@ -0,0 +1,201 @@
+---
+title: "Session Log Reference"
+description: >
+  Reference for the session log exported with aNCA results.
+  Describes what events are captured, log levels, and configuration.
+output: rmarkdown::html_vignette
+vignette: >
+  %\VignetteIndexEntry{Session Log Reference}
+  %\VignetteEngine{knitr::knitr}
+  %\VignetteEncoding{UTF-8}
+---
+
+When you export results as a ZIP file, aNCA includes a `session_log.txt` that
+records application events from your session. This page explains what the log
+contains, how to read it, and how to configure its verbosity.
+
+## What the log captures
+
+The session log records events emitted by explicit logging calls placed
+throughout the aNCA Shiny application. Each line follows this format:
+
+```
+[2025-04-30 09:40:16] INFO: Calculating NCA results...
+```
+
+The log captures **application-level events** — not raw R console output.
+Only messages that pass through aNCA's internal `log_*()` functions appear
+in the file.
+
+### What is NOT captured
+
+- Unexpected R warnings or errors that are not wrapped in a `tryCatch` block
+  with a corresponding `log_warn()` or `log_error()` call.
+- Messages from third-party packages (e.g., `PKNCA`, `dplyr`) unless the
+  application explicitly catches and logs them.
+- Raw `cat()` or `print()` output from any source.
+
+## Log levels
+
+aNCA uses six log levels, ordered from most to least verbose:
+
+| Level | Purpose |
+|---|---|
+| **TRACE** | Fine-grained internal operations (module attachment, reactive updates) |
+| **DEBUG** | Detailed diagnostic data (parameter lists, slope rule dumps) |
+| **INFO** | Key user-facing operations (data upload, NCA calculation, setting changes) |
+| **SUCCESS** | Completion confirmations (data loaded, results calculated) |
+| **WARN** | Non-fatal issues (calculation warnings, incompatible settings) |
+| **ERROR** | Failures (calculation errors, file load failures) |
+
+The default threshold is **INFO**, meaning only INFO, SUCCESS, WARN, and ERROR
+messages appear. Set `aNCA_LOG_LEVEL=TRACE` or `aNCA_LOG_LEVEL=DEBUG` in your
+`.Renviron` file to see more detail.
+
+## Logged events by workflow stage
+
+The following table lists all events currently captured in the session log,
+organized by the stage of the workflow where they occur.
+
+### Startup
+
+| Event | Level |
+|---|---|
+| Application startup | INFO |
+| Application restarting | INFO |
+
+### Data Upload
+
+| Event | Level |
+|---|---|
+| Data upload initialized (with file path) | INFO |
+| All user data loaded | SUCCESS |
+| File loading errors | ERROR |
+| User data binding errors | ERROR |
+
+### Settings Restore
+
+| Event | Level |
+|---|---|
+| Settings restored from version | SUCCESS |
+| Settings loaded from file | SUCCESS |
+| Settings load failure | ERROR |
+| Incompatible settings (analyte, profile, specimen) | WARN |
+
+### Data Mapping
+
+| Event | Level |
+|---|---|
+| Processing data mapping | INFO |
+| Data mapping warnings | WARN |
+| Data mapping errors | ERROR |
+
+### Data Filtering
+
+| Event | Level |
+|---|---|
+| Data filtering warnings | WARN |
+
+### NCA Settings
+
+| Event | Level |
+|---|---|
+| Analyte selection changed | INFO |
+| Specimen selection changed | INFO |
+| NCA profile selection changed | INFO |
+| Extrapolation method changed | INFO |
+| Min. half-life points changed | INFO |
+| Flag rule enabled/disabled | INFO |
+| Flag rule threshold changed | INFO |
+| BLQ imputation strategy changed | INFO |
+| Start concentration imputation toggled | INFO |
+
+### Parameter Selection
+
+| Event | Level |
+|---|---|
+| Parameter count per study type | INFO |
+| Full parameter list per study type | DEBUG |
+
+### Slope Selector
+
+| Event | Level |
+|---|---|
+| Module server attachment | TRACE |
+| Plotly click detected | TRACE |
+| Manual slope rule added | INFO |
+| Manual slope rule removed | INFO |
+| Slope rules summary (inclusions/exclusions count) | DEBUG |
+| Manual slopes override applied | DEBUG |
+| Manual slopes override incompatible | WARN |
+| Slope edit table rendering | TRACE |
+
+### General Exclusions
+
+| Event | Level |
+|---|---|
+| Exclusion added (row count, type, reason) | INFO |
+| Exclusion removed | INFO |
+| Exclusions restored from settings | INFO |
+
+### NCA Calculation
+
+| Event | Level |
+|---|---|
+| Creating / updating PKNCA data object | TRACE |
+| PKNCA data object created | SUCCESS |
+| PKNCA data object creation error | ERROR |
+| Updating parameter selection data | TRACE |
+| Calculating NCA results | INFO |
+| NCA calculation warnings | WARN |
+| NCA results calculated | SUCCESS |
+| NCA calculation error | ERROR |
+| Invalid parameters | ERROR |
+
+### Exploration Plots
+
+| Event | Level |
+|---|---|
+| Rendering individual plots | INFO |
+| Computing mean plot | INFO |
+| Rendering boxplot | INFO |
+| Exploration plot saved (with overwrite flag) | INFO |
+| Exploration plot removed | INFO |
+
+### TLG Generation
+
+| Event | Level |
+|---|---|
+| TLG module server attachment | TRACE |
+| Submitted TLG list | DEBUG |
+| TLG list rendering error | ERROR |
+
+### Export
+
+| Event | Level |
+|---|---|
+| Downloading summary statistics as CSV | INFO |
+
+### Units & Other
+
+| Event | Level |
+|---|---|
+| Applying custom units specification | TRACE |
+
+## Configuring the log level
+
+Set the `aNCA_LOG_LEVEL` environment variable before starting the app.
+Valid values: `TRACE`, `DEBUG`, `INFO` (default), `SUCCESS`, `WARN`, `ERROR`.
+
+In your `.Renviron` file:
+
+```
+aNCA_LOG_LEVEL=DEBUG
+```
+
+Or set it in R before launching:
+
+```r
+Sys.setenv(aNCA_LOG_LEVEL = "TRACE")
+aNCA::run_app()
+```